Duodenal tuberculosis with gastric outlet obstruction: a case report of successful diagnosis and treatment, with review of literature

BACKGROUND

Duodenal tuberculosis (TB) is extremely rare, and its diagnosis is challenging owing to the lack of specific symptoms and radiological or endoscopic findings. When it leads to gastric outlet obstruction (GOO), diagnosing it accurately and providing appropriate treatment is crucial. However, this is often overlooked.

CASE PRESENTATION

A 35-year-old man presented with abdominal pain, fullness, vomiting, and weight loss. Upper gastrointestinal endoscopy and radiography revealed nearly pinpoint stenosis with edematous and reddish mucosa in the D1/D2 portion of the duodenum. Computed tomography (CT) showed the duodenal wall thickening, luminal narrowing, multiple enlarged abdominal lymph nodes, and portal vein stenosis. Conventional mucosal biopsy during endoscopy revealed ulcer scars. We initially suspected stenosis due to peptic ulcers; however, chest CT revealed cavitary lesions in both lung apices, suggesting tuberculosis. Due to the suspicion of duodenal TB and the need to obtain deeper tissue samples, endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) was performed. The tissue sample showed caseating granulomas with multinucleated giant cells, and acid-fast bacilli were positive by Ziehl-Neelsen staining. The patient was diagnosed with duodenal TB and subsequent GOO. Because the patient had difficulty eating, surgical intervention was prioritized over antitubercular drugs, and laparoscopic gastrojejunostomy was performed. The patient started an oral diet on the 3rd postoperative day and began antitubercular treatment immediately after discharge on the 11th day. During the 6th month of treatment, endoscopic examination revealed residual duodenal stenosis; however, the bypass route functioned well, and the patient remained asymptomatic.

CONCLUSIONS

An aggressive biopsy should be performed to diagnose duodenal TB. EUS-FNA has proven to be a useful tool in this regard. Both nutritional improvement and antitubercular treatment were achieved early and reliably by performing laparoscopic gastrojejunostomy for duodenal TB with GOO.

Efficacy of early clip-with-line method for colorectal endoscopic submucosal dissection

BACKGROUND

Colorectal endoscopic submucosal dissection (ESD) remains demanding due to technical difficulties and high risk of perforation. Most of the reported traction methods are initiated after creating a mucosal flap, which is time consuming. To obtain a good visualization at the mucosal incision stage, we developed the early clip-with-line (ECL) method. This method was started immediately after injection of sodium hyaluronate solution into the submucosal layer. In this study, we evaluated the efficacy and the safety of the ECL method for colorectal ESD.

METHODS

We retrospectively analyzed all cases of colorectal ESDs (41 cases in total) performed from January 2017 to February 2019 in our institution. From January 2017 to August 2018, 27 of these cases were performed using conventional (non-ECL) ESDs, while from September 2018 onwards, the remaining 14 cases were performed using the ECL method. Retrospective comparison between the ECL group and the non-ECL group was conducted in terms of clinical characteristics, treatment outcomes, and adverse events.

RESULTS

There were no significant differences in clinical characteristics between two groups. Procedure time (median [range]) was significantly shorter in the ECL group than in the non-ECL group (66 [29-131] min vs 90 [30-410] min; P = 0.03). As for adverse events, no case of perforation occurred in the ECL group, whereas perforation was observed in 7.4% (2/27) cases in the non-ECL group (no significant difference).

CONCLUSION

Early clip-with-line method for colorectal endoscopic submucosal dissection reduced procedure time.

Factors affecting the accuracy of endoscopic transpapillary sampling methods for bile duct cancer

BACKGROUND AND AIM

Various methods for endoscopic transpapillary sampling have been developed. However, the factors affecting the accuracy of these methods for bile duct cancer are unknown. The aim of the present study was to determine the factors affecting the accuracy of endoscopic transpapillary sampling methods.

METHODS

We reviewed the results from 101 patients with bile duct cancer who underwent transpapillary sampling by aspiration bile cytology, brushing cytology, and fluoroscopic forceps biopsy. The final diagnosis of bile duct cancer was made on the basis of pathological evaluation of specimens obtained at surgery and the clinical course over at least 1 year in patients not operated on. We carried out subgroup analyses for the factors affecting the accuracy of each transpapillary sampling method.

RESULTS

Aspiration bile cytology was carried out 238 times in 77 patients, brushing cytology was carried out 67 times in 60patients, and fluoroscopic forceps biopsy was carried out 64 times in 53 patients. Accuracies of aspiration bile cytology were significantly higher for longer (≥15 mm) biliary cancerous lesions than for shorter (<15 mm) lesions (30% vs 18%, respectively, P = 0.049). Accuracies of brushing cytology and fluoroscopic forceps biopsy were significantly higher for non-flat than for flat-type biliary cancerous lesions (brushing: 58% vs 38%, respectively, P = 0.032; forceps biopsy: 60% vs 33%, respectively, P = 0.043).

CONCLUSION

Endoscopic transpapillary sampling methods are more accurate for longer or elevated (non-flat) biliary cancerous lesions than for shorter or flat lesions.

Randomized controlled study of gemcitabine plus S-1 combination chemotherapy versus gemcitabine for unresectable pancreatic cancer

PURPOSE

The aim of this study was to evaluate efficacy and safety of gemcitabine plus S-1 (GS) combination chemotherapy in patients with unresectable pancreatic cancer.

METHODS

Patients were randomly assigned to receive GS (oral S-1 60 mg/m(2) daily on days 1-15 every 3 weeks and gemcitabine 1,000 mg/m(2) on days 8 and 15) or gemcitabine (1,000 mg/m(2) on days 1, 8, and 15 every 4 weeks). The primary endpoint was progression-free survival (PFS).

RESULTS

One hundred and one patients were randomly assigned. PFS was significantly longer in the GS arm with an estimated hazard ratio (HR) of 0.65 (95 % CI 0.43-0.98; P = 0.039; median 5.3 vs 3.8 months). Objective response rate (ORR) was also better in the GS arm (21.6 vs 6 %, P = 0.048). Median survival was 8.6 months for GS and 8.6 months for GEM (HR 0.93; 95 % CI 0.61-1.41; P = 0.714). Grade 3-4 neutropenia (44 vs 19.6 %, P = 0.011) and thrombocytopenia (26 vs 8.7 %, P = 0.051) were more frequent in the GS arm.

CONCLUSIONS

GS therapy improved PFS and ORR with acceptable toxicity profile in patients with unresectable pancreatic cancer.

Clinical usefulness of repeated pancreatic juice cytology via endoscopic naso-pancreatic drainage tube in patients with pancreatic cancer

BACKGROUND

Cytological examination of pancreatic juice obtained during endoscopic retrograde cholangiopancreatography (ERCP) is well established, but its sensitivity for pancreatic cancer has not been satisfactory. The aim of this study was to evaluate the usefulness of repeated pancreatic juice cytology (PJC) via the endoscopic naso-pancreatic drainage (ENPD) tube in patients with pancreatic cancer compared with conventional PJC.

METHODS

We retrospectively investigated 139 patients with pancreatic disease. Between April 2004 and November 2007, conventional PJC was performed in 56 patients with pancreatic cancer and 23 with benign pancreatic stricture. Between January 2008 and November 2010, ENPD was used in 40 patients with pancreatic cancer and 20 with benign pancreatic stricture. The ENPD tube was placed into the main pancreatic duct for up to 3 days, and cytological samples of pancreatic juice were collected up to 6 times in total.

RESULTS

Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of the ENPD method for pancreatic cancer were 80, 100, 100, 71, and 87 %, respectively, revealing significantly higher sensitivity than the conventional method (p = 0.0001). Sensitivities according to tumor location and size were 90 % (19/21), 69 % (9/13), and 67 % (4/6) in the head, body, and tail of the pancreas, 88 % (7/8), 79 % (19/24), and 75 % (6/8) in tumors with a diameter less than 20 mm including carcinoma in situ, 21-40, and greater than 41 mm, respectively.

CONCLUSIONS

The ENPD method was found to have high diagnostic yield, especially for tumors less than 20 mm or located in the pancreatic head, and might be useful for the diagnosis of early-stage pancreatic cancer.

Current situation of endoscopic treatment for common bile duct stones

BACKGROUND/AIMS

The progression of endoscopy and devices as well as newly developed treatment methods have enabled endoscopic lithotomy. In this study, we examined to what degree is it possible to endoscopically treat patients who are diagnosed as having common bile duct stones.

METHODOLOGY

Lithotomy was conducted using a backward side-viewing endoscope for patients without surgical history of upper gastrointestinal tract and patients with stomach reconstructed with Billroth-I method, using an ordinary endoscope for patients with stomach reconstructed with Billroth-II method (Bil-II) and using a double balloon endoscope for patients with difficulty in reaching the papilla or patients of Roux-en-Y anastomosis (R-Y). As for treatment methods, we selected endoscopic sphincterotomy as the first choice for papilla treatment and selected endoscopic papillary balloon dilation for patients with bleeding tendency or patients of Bil-II or R-Y. For patients with multiple stones or giant stones, lithotripsy was selected depending on judgment of the endoscopist.

RESULTS

Endoscopic complete lithotomy was successful in 97.7% (168/172). An accidental disease was observed in 2.9% (5/172). In one patient with the perforated gastrointestinal tract, a surgery was performed but others were mild.

CONCLUSIONS

Common bile duct stones can be endoscopically treated safely with high rate.

Abstract A39: The exploration of novel strategy for treatment of pancreactic ductal adenocarcinoma targeting tumor microenvironment with multi-kinase inhibitors

Background and Aim: Pancreatic ductal adenocarcinoma (PDAC) is an almost uniformly lethal disease in humans. Previously, we have reported a genetically engineered mouse PDAC progression model which has pancreatic-specific transforming growth factor-beta receptor type II knockout in the context of Kras activation (Ijichi H, et al 2006). This model shows PDAC with 100% penetrance and recapitulates the signature of human PDAC well. Using this model, we explored novel treatment for PDAC.

Materials and Methods: At first, to investigate whether the mice model is suitable for the drug screening, the mice were treated with gemcitabine (12.5 mg/kg) by intraperitoneal (i.p.) injection or S-1 (8.4 mg/kg) per oral, which are the standard drug for human PDAC. To the next, for single agent treatment, mice were treated orally 6 times a week with vehicle (0.5 % carboxymethyl cellulose, CMC), sunitinib (40 mg/kg), and axitinib (30mg/kg), both of which are multikinase inhibitors targeting vascular endothelial growth factor receptor (VEGFR) and platelet derived growth factor receptor (PDGFR) from the 3 weeks of age. For combined agent experiment, mice were treated orally with vehicle (0.5 % CMC) or axitinib from the 3 weeks of age and also treated with saline or gemcitabine, i.p. twice a week from the 4 weeks of age. Treatment continued until 8 weeks of age. Moreover, for the survival analysis, the drug treatment was continued until the mice became distressed according to the same schedule stated above. In vivo anti-tumor effect and survival time were assessed. Immunostaining of tumor tissue for caspase 3, Ki67, CD31, F4/80 and VEGF was performed. Azan staining also performed for the assessment of fibrosis in the tumor.

Results: Gemcitabine and S-1 showed antiproliferative effect and prolonged overall survival of these mice compared to control, as well as human cases. Median survival time of single use of axtinib and sunitinib group was significantly longer (p &lt;0.01) than that of control group. Axitinib and sunitinib group showed significantly stronger anti-tumor effect in vivo (p &lt;0.01). In the combined treatment experiment, gemcitabine plus axitinib-treated group showed statistically significant longer survival and more anti-tumor effect than that of gemcitabine or axtinib alone-treated group (p &lt;0.01). Axitinib and sunitinib group showed significantly higher caspase 3 stainng and lower Ki67 staining than that of control (p &lt;0.01). Microvessel density (CD 31 staining) of axitinib and sunitinib group was significantly lower than that of control (p &lt;0.01). F4/80 staining was significantly lower in axitinib and sunitinib-treated group than that of control (p &lt;0.05). VEGF expression of axitinib and sunitinib group was significantly lower than that of control a (p &lt;0.001). Azan staining showed significantly lower fibrosis in axitinib and sunitinib-treated group compared to control (p &lt;0.01).

Conclusion: Targeting not only cancer cells but also tumor microenvironment, such as angiogenesis, infiltration of immune cells, and fibrosis, with the use of multikinase inhibitors in addition to gemcitabine, may be a promising therapeutics for PDAC.

Comparative risk of common peroneal nerve injury in far anteromedial portal drilling and transtibial drilling in anatomical double-bundle ACL reconstruction

PURPOSE

The purpose of this study was to investigate the risk of common peroneal nerve injury in FM drilling as compared to transtibial drilling in anatomical double-bundle ACL reconstruction.

METHODS

Ten cadaveric knees without ligament injury or significant arthritis were used for this study. Knees were secured at 90° and 120° of flexion. In transtibial drilling groups, a guide pin was drilled through either the anteromedial bundle (AMB) or posterolateral bundle (PLB) tibial insertion site to either the AMB or PLB femoral insertion site (tibial insertion site-femoral insertion site: AM-AM, PL-PL, PL-AM and AM-PL). In FM drilling groups (FM-AM and FM-PL),the pin was drilled at the AMB or PLB femoral insertion site through the FM. We measured the shortest distance between the point at which the pin ran through the lateral cortex of the femur and the ipsilateral common peroneal nerve at a knee flexion of 90° and 120°.

RESULTS

At a knee flexion of 90°, the shortest mean distance to the common peroneal nerve was 15.3 mm in the FM-PL group, 13.4 mm in the FM-AM group, 27.9 mm in the PL-PL group, 30.8 mm in the AM-AM group, 37.8 mm in the PL-AM group and 29.5 mm in the AM-PL group. At a knee of flexion 120°, the mean distance was 17.3 mm in the FM-PL group, 18.1 mm in the FM-AM group, 32.2 mm in the PL-PL group, 36.6 mm in the AM-AM group, 38.0 mm in the PL-AM group and 35.2 mm in the AM-PL group. Significant differences were observed between 90° and 120° of knee flexion in the FM-AM, PL-PL, AM-AM and AM-PL groups (P < 0.05). Significant differences were observed at flex 90° between the FM-AM group and AM-AM group, and between the FM-AM group and PL-AM group. Significant differences were observed at flex 120° between the FM-AM group and AM-AM group, between the FM-AM group and PL-AM group and between the FM-PL group and AM-PL group.

CONCLUSION

The distance to the peroneal nerve in FM drilling was significantly longer at 120° than at 90° of knee flexion. Therefore, the risk of peroneal injury using FM drilling should decrease at a higher angle of knee flexion.

Transpancreatic precut papillotomy in patients with difficulty in selective biliary cannulation

BACKGROUND/AIMS

Transpancreatic precut papillotomy (TPPP) is considered as an effective method in patients with difficulty in selective biliary cannulation. However, the use of placing a pancreatic duct stent as a measure against post-ERCP pancreatitis has not been clarified. Here we examine the methods of implementing TPPP safely.

METHODOLOGY

TPPP was conducted on patients with difficulty in selective biliary cannulation. The incidence of pancreatitis was compared between group P(+) in which a spontaneous dislodgement type pancreatic duct stent was placed and group P(-) without a duct stent.

RESULTS

The success rate of biliary cannulation was 83.3% at the first ERCP and finally 93.9%. Post-ERCP pancreatitis was observed in 9.09% of patients. The success rate of placement of pancreatic duct stent in the P(+) group was 100%. The incidence of pancreatitis in the P(+) group was 4.1% and the mean post-ERCP amylase level was 340.071 ±420.035IU/L. The incidence of pancreatitis in the P(-) group was 23.5% and the mean post-ERCP amylase level was 661.250±772.285IU/L. The incidence of pancreatitis and the mean post-ERCP amylase level were significantly lower in the P(+) group (p<0.05).

CONCLUSIONS

In the patients with difficulty in selective biliary cannulation, TPPP is a useful technique for biliary cannulation. The placement of a spontaneous dislodgement type pancreatic duct stent after TPPP may be useful for prevention of post-ERCP pancreatitis.

A long-term controlled trial of endoscopic pancreatic stenting for treatment of main pancreatic duct stricture in chronic pancreatitis

BACKGROUND/AIMS

Endoscopic pancreatic stenting (EPS) has been used to treat main pancreatic duct (MPD) stricture in chronic pancreatitis (CP), with favourable reported results. However, most studies were retrospective and uncontrolled. We conducted a longterm prospective controlled study of EPS for treatment of MPD stricture in CP.

METHODOLOGY

Consecutive patients with CP were treated to remove pancreatic stones by extracorporeal shock-wave lithotripsy or endoscopic basket extraction. After treatment, 41 patients were enrolled in the study upon meeting the criteria of complete removal of stones, pain relief after the treatment, and dominant stricture of the MPD. Twenty patients chose EPS, while 22 control patients did not. We compared recurrence of pain and pancreatic function between groups for over 3 years of follow-up.

RESULTS

The mean follow-up period was 62.5 ± 20.9 months. Pain recurred in 15% of EPS patients (3/20) and in 50.0% of control patients (11/22), a significant difference (p<0.05). Progression of exocrine insufficiency in the EPS group was significantly slower than in the control group (p<0.05), while endocrine function showed no difference between groups.

CONCLUSIONS

EPS reduced pain recurrence and slowed down the progression of exocrine insufficiency in CP patients with MPD stricture.

New cannulation method for pancreatic duct cannulation-bile duct guidewire-indwelling method

The patient was a 58-year-old male with symptomatic alcoholic chronic pancreatitis. Since a 10 mm calculus was observed in the pancreatic body and abdominal pain occurred due to congestion of pancreatic juice, endoscopic retrograde cholangiopancreatography was conducted for assessment of the pancreatic duct and treatment of pancreatic calculus. Pancreatogram was slightly and insufficiently obtained by injecting the contrast media via the common channel of the duodenal main papilla. We tried to cannulate selectively into the pancreatic duct for a clear image. However, the selective cannulation of the pancreatic duct was difficult because of instability of the papilla. On the other hand, selective cannulation of the bile duct was relatively easily achieved. Therefore, after the imaging of the bile duct, a guidewire was retained in the bile duct to immobilize the duodenal papilla and cannulation of the pancreatic duct was attempted. As a result, selective pancreatic duct cannulation became possible. It is considered that the bile duct guidewire-indwelling method may serve as one of the useful techniques for cases whose selective pancreatic duct cannulation is difficult (“selective pancreatic duct difficult cannulation case”).

Utility of placement of pancreatic duct spontaneous dislodgement stent for prevention of post-ERCP pancreatitis in patients with difficulty in selective biliary cannulation

BACKGROUND/AIMS

To examine the utility of placement of pancreatic duct spontaneous dislodgement stents for prevention of post-ERCP pancreatitis in patients with difficulty in selective biliary cannulation.

METHODOLOGY

The incidence of pancreatitis was compared between the group with P(+) pancreatic duct spontaneous dislodgement stent placed for prevention of post-ERCP pancreatitis and the group without P(-) in patients with difficulty in selective biliary cannulation.

RESULTS

The final success rate of selective biliary cannulation was 94.45%. Post-ERCP pancreatitis was observed at 7.07%. The success rate of placement of pancreatic duct stent in the P(+) group was 99.0%. The incidence of pancreatitis in 99 patients in the P(+) group was 3.0%, that of abdominal pain was 3.0%, that of hyperamylasemia was 16.2%, and the mean post-ERCP amylase level was 353.031 +/- 520.792 IU/L. The incidence of pancreatitis in the P(-) group was 11.1%, that of abdominal pain was 20.2%, that of hyperamylasemia was 33.3%, and the mean post-ERCP amylase level was 541.204 +/- 771.843 IU/L. Comparing between the P(+) group and P(-) group, the incidence of pancreatitis, that of abdominal pain, that of hyperamylasemia and the mean post-ERCP amylase level were significantly decreased in the P(+) group (p<0.05).

CONCLUSION

Placement of pancreatic duct spontaneous dislodgement stent in patients with difficulty in selective biliary cannulation could be useful for prevention of post-ERCP pancreatitis.

Quantitative analysis of vascular endothelial growth factor in liver metastases from pancreatic carcinoma as a predictor of chemotherapeutic effect and prognosis

PURPOSE

In pancreatic carcinoma, vascular endothelial growth factor (VEGF) expression at the primary site has been suggested to be a prognostic parameter. We quantitatively analyzed VEGF expression in liver metastases from pancreatic carcinoma and examined the correlation among VEGF expression in liver metastases, clinicopathologic factors, and clinical outcome.

EXPERIMENTAL DESIGN

The subjects consisted of 23 patients with pancreatic adenocarcinoma who had liver metastases and were treated with S-1 and gemcitabine as the first-line treatment. VEGF expression was quantitated by enzyme immunoassay in biopsy specimens of liver metastases and nontumorous liver tissue, and in plasma. In 10 of the 23 patients, VEGF expression was also quantitated in biopsy specimens of the primary pancreatic tumor. All samples were collected before treatment.

RESULTS

The VEGF level in nontumorous liver tissue was 36.6 +/- 10.0 pg/mg protein versus 376.8 +/- 106.1 pg/mg protein in liver metastases (P = 0.0016). Pretreatment VEGF levels in plasma and in primary pancreatic carcinoma did not correlate with VEGF levels in the corresponding liver metastases. The median VEGF level in liver metastases (138.9 pg/mg protein) was used as the cutoff value between high and low VEGF expression in liver metastases. Patients showing high VEGF expression had a significantly longer progression-free survival and overall survival than patients showing low VEGF expression in liver metastases (P = 0.0219 and P = 0.0074, respectively).

CONCLUSIONS

Evaluation of VEGF levels in liver metastases might be useful in assessing the prognosis of patients with metastatic pancreatic carcinoma who are under systemic chemotherapy.

Molecular motors: thermodynamics and the random walk

The biochemical cycle of a molecular motor provides the essential link between its thermodynamics and kinetics. The thermodynamics of the cycle determine the motor's ability to perform mechanical work, whilst the kinetics of the cycle govern its stochastic behaviour. We concentrate here on tightly coupled, processive molecular motors, such as kinesin and myosin V, which hydrolyse one molecule of ATP per forward step. Thermodynamics require that, when such a motor pulls against a constant load f, the ratio of the forward and backward products of the rate constants for its cycle is exp [-(DeltaG + u(0)f)/kT], where -DeltaG is the free energy available from ATP hydrolysis and u(0) is the motor's step size. A hypothetical one-state motor can therefore act as a chemically driven ratchet executing a biased random walk. Treating this random walk as a diffusion problem, we calculate the forward velocity v and the diffusion coefficient D and we find that its randomness parameter r is determined solely by thermodynamics. However, real molecular motors pass through several states at each attachment site. They satisfy a modified diffusion equation that follows directly from the rate equations for the biochemical cycle and their effective diffusion coefficient is reduced to D-v(2)tau, where tau is the time-constant for the motor to reach the steady state. Hence, the randomness of multistate motors is reduced compared with the one-state case and can be used for determining tau. Our analysis therefore demonstrates the intimate relationship between the biochemical cycle, the force-velocity relation and the random motion of molecular motors.

Small molecular mass inhibitor of growth of MDCK cells derived from pig spinal cord

We have discovered cell growth inhibitory activity in a salt extract of pig spinal cords. The growth inhibitory factor was purified by gel-filtration, ion-exchange and high performance liquid chromatography. Incubation of MDCK cells with the inhibitor arrested their locomotion within half an hour, suppressed their proliferation, and caused them to become round. The round cells that were still attached to the culture plate were alive. Upon removal of the inhibitor these cells flattened out and resumed locomotion and proliferation. The inhibitor was 100 times less effective on CHO-K1 cells. The reversible effects of the inhibitor on MDCK cells and its little effects on CHO-K1 cells indicate that the inhibitory activity is not due to a non-specific toxic mechanism. The inhibitor was both heat-stable and resistant to several chemical treatments, including proteases. Its behavior upon ion exchange chromatography suggested that it was positively charged at neutral pH, whilst its molecular mass was estimated to be 350 or larger by gel-filtration FPLC analysis. The inhibitory fraction reacted extensively with fluorescamine, suggesting that the inhibitory factor has amine groups, which are a possible candidate for its positive charges. Since spermine and spermidine, unlike the inhibitor in the present study, irreversibly inhibited the growth of the MDCK cells, the inhibitory activity in the present study is thus not due to contamination by these polyamines. Our experiments also support that the inhibitor is not a peptide.

Fluctuations in sliding motion generated by independent and random actions of protein motors

We consider theoretical fluctuations in the in vitro sliding movement of individual cytoskeletal filaments generated by an ensemble of protein motors whose actions are assumed to be statistically independent and random. We show that the mean square deviation of the sliding distances of a filament for a given period of time around their average is proportional to the inverse of the filament length. This result provides a basis for an experimental test of the general assumption on the independent and random actions of protein motors.

A protein friction model of the actin sliding movement generated by myosin in mixtures of MgATP and MgGTP in vitro

The sliding movement of an actin filament generated by myosin heads with MgGTP bound is much slower than that by those with MgATP bound. Nonetheless, there is a report that the actin sliding velocity at low (11-21 microM) MgATP concentrations is increased by the addition of MgGTP in a range of 1-3 mM, although the actin sliding velocity at these MgATP concentrations is larger than the maximum sliding velocity attained in the presence of MgGTP alone. The convex rise in the velocity was called "mutual sensitization of MgATP and MgGTP" in the report. Here we propose a theoretical model to account for the mutual sensitization of MgATP and MgGTP. The model is an extension of a protein friction model, accommodating the presence of two different substrates and assuming the presence of motile and non-motile myosins. This new model is in accord with the characteristics of the actin/myosin sliding movement experimentally observed in mixtures of MgATP and MgGTP. Comparison of the model with the experimental results implies that the non-motile and motile myosins are those with the "converse and correct" orientations of their heads with respect to the direction of the actin sliding movement in vitro.

Synchronous firing patterns of a set of insect neurosecretory cells

The number of active cells in each synchronous firing event in a set of 10 neurosecretory cells in the silkmoth Bombyx mori was estimated from the amplitude and waveform of compound action potentials. One to 10 cells discharged an action potential within a period of 30 ms and one to two or nine to 10 units became active more frequently in a synchronous firing event. Numbers of active cells fluctuated like a sequence of pseudo random numbers, though the same number of cells tended to fire in two successive firing events of a short interval. These patterns suggest that electrical coupling may mediate synchronous firings in the insect neurosecretory cell system.

Fluctuation correlation in the sliding movement generated by protein motors in vitro

The fluctuation in the sliding distance of cytoskeletal filaments driven to move by protein motors in vitro does not depend on the filament length. This is in sharp contrast to the case of Brownian movement of filamentous particles in their longitudinal directions, in which the positional fluctuation is proportional to the inverse of the length (L) of filaments. This latter 1/L dependence is a direct consequence of the central limit theorem: the statistical independence and randomness of the solvent molecule collisions with filaments, the collisions of which cause the random Brownian movement. The above length-independence in the sliding distance fluctuation found in the in vitro motility indicates the presence of correlation in the fluctuation. A possible explanation for the correlation is to assume that there is an extended time-correlation in the sliding movement, a correlation which could be produced by the actions on a sliding filament of protein motors with their heads randomly oriented in the in vitro motility assay system. We have checked this possibility by using long myosin thick filaments of molluscan smooth muscles, on which myosin heads are uniformly oriented, and have found that even with such myosin filaments with oriented myosin heads, the positional fluctuation of actin sliding distance does not depend on the actin filament length. This result thus indicates that the actions of protein motors on a sliding filament are not statistically independent or random, so that the positional fluctuation of filaments in the motor-generated sliding movement does not depend on the filament length.

Length dependence of displacement fluctuations and velocity in microtubule sliding movement driven by sea urchin sperm outer arm β dynein in vitro

We have studied the dependence on microtubule length of sliding velocity and positional fluctuation from recorded trajectories of microtubules sliding over sea urchin sperm outer arm beta dynein in a motility assay in vitro. The positional fluctuation was quantified by calculating the mean-square displacement deviation from the average, the calculation of which yields an effective diffusion coefficient. We have found that (1) the sliding velocity depends hyperbolically on the microtubule length, and (2) the effective diffusion coefficients do not depend on the length for sufficiently long microtubules. The length dependence of the sliding velocity indicates that the duty ratio, defined as the force producing period over the total cycle time of beta dynein interaction with microtubule, is very small. The length independence of the effective diffusion coefficient indicates that there is a correlation in the sliding movement fluctuation of microtubules.

Force production by chemically crosslinked myosin-actin crossbridges in rabbit skinned fibers in response to MgATP depletion

In order to study the contractile property of myosin crossbridges attached to thin filaments, myosin heads were crosslinked to the filaments at their interface in single skinned rabbit psoas fibers with a zero-length chemical crosslinker, 1-(3-dimethylamino-propyl)-3-ethylcarbodiimide (EDC). The results obtained show that a partially crosslinked single fiber produces a large rigor-like force when MgATP is depleted from the myofibrillar space. Such crosslinked fibers contain two types of crosslinked myosin heads: one with one of the two heads of the myosin molecule crosslinked to actin with the other head uncrosslinked; the other has both heads crosslinked to actin. The results of this work suggest that a crosslinked myosin head of the former type produces a much larger force than the latter type.

Monte Carlo study for fluctuation analysis of the in vitro motility driven by protein motors

The fluctuation properties of the sliding movement of an individual cytoskeletal filament driven by protein motors in vitro can be analyzed by calculating the mean-square deviation of the displacement from the average within its single trajectory. For this purpose, a Monte Carlo simulation was used to define the conditions and limitations of a method for smoothing (curved) noisy trajectories without affecting either the steady or fluctuation characteristics inherent to the individual filament sliding movement. By applying the method to real experimental trajectory data, we show that an effective diffusion coefficient from displacement fluctuations of a sliding filament can be obtained from its single noisy trajectory even when it is curved.

Fluctuation in the microtubule sliding movement driven by kinesin in vitro

We studied the fluctuation in the translational sliding movement of microtubules driven by kinesin in a motility assay in vitro. By calculating the mean-square displacement deviation from the average as a function of time, we obtained motional diffusion coefficients for microtubules and analyzed the dependence of the coefficients on microtubule length. Our analyses suggest that 1) the motional diffusion coefficient consists of the sum of two terms, one that is proportional to the inverse of the microtubule length (as the longitudinal diffusion coefficient of a filament in Brownian movement is) and another that is independent of the length, and 2) the length-dependent term decreases with increasing kinesin concentration. This latter term almost vanishes within the length range we studied at high kinesin concentrations. From the length-dependence relationship, we evaluated the friction coefficient for sliding microtubules. This value is much larger than the solvent friction and thus consistent with protein friction. The length independence of the motional diffusion coefficient observed at sufficiently high kinesin concentrations indicates the presence of correlation in the sliding movement fluctuation. This places significant constraint on the possible mechanisms of the sliding movement generation by kinesin motors in vitro.

Tension relaxation induced by pulse photolysis of caged ATP in partially crosslinked fibers from rabbit psoas muscle

Muscle contractile force is thought to be generated by ATP-induced conformational changes in myosin crossbridges. In the present study, we investigated the response to ATP binding of force-bearing, attached cross-bridges. For this investigation, skinned fibers, in which myosin heads were in part covalently crosslinked to thin filaments with a zero-length crosslinker, were prepared. Caged ATP [the P3-1-(2-nitro)phenylethyl ester of ATP] was then pulse-photolyzed in these crosslinked fibers, which retained ATP-induced "rigor" tension, and then the subsequent tension changes were followed at 14-16 degrees C and ionic strengths of 0.1-2 M. A rapid tension decrease was observed after the photolysis in the partially crosslinked fibers. The rate of the decrease was not any different from that in the uncrosslinked fibers compared at ionic strength of 0.2 M. This and other results thus indicate a kinetic similarity in the crosslinked and uncrosslinked crossbridges in response to ATP binding. These findings also suggest that ATP-induced structural changes take place in the attached crossbridges at a rate similar to that of the ATP-induced dissociation of crossbridges from thin filaments.

Trinitrophenylation of the reactive lysine residue in double-headed myosin in the presence of PP

Lys-83 in the heavy chain of rabbit skeletal muscle myosin is rapidly and stoichiometrically modified by trinitrobenzene sulfonate. Other authors claimed that the half-stoichiometric trinitrophenylation of Lys-83 in myosin in the presence of PPi was correlated to a Pro/Ser microheterogeneity at the 78th residue position in the heavy chain [Miyanishi, T., Maita, T., Matsuda, G., & Tonomura, Y. (1982) J. Biochem. 91, 1845-1853]. However, our recent studies with chymotryptic subfragment 1 (S1) instead of myosin showed no such correlation between the half-stoichiometric trinitrophenylation and the Pro/Ser microheterogeneity [Komatsu, H. & Tawada, K. (1993) J. Biol. Chem. 268, 16974-16978]. Since the global structure of the head portion of myosin is different from that of chymotryptic S1 that lacks DTNB light chain, it could be argued that the difference is due to the structural difference between chymotryptic S1 and myosin. We hence reexamined the situation with myosin, and obtained the same results as found with S1: (i) Lys-83 in myosin was half-stoichiometrically trinitrophenylated in the presence of PPi, although it was stoichiometrically modified in the absence of PPi; (ii) there was a Pro/Ser microheterogeneity at the 78th position in the myosin heavy chain, which was not correlated to the half-stoichiometric trinitrophenylation of Lys-83 in the presence of PPi.

Microheterogeneity around the reactive lysine residue in the myosin heavy chain from rabbit skeletal muscle

A molecule of myosin subfragment 1 (S1) from rabbit skeletal muscle has one highly reactive lysine residue, Lys-83 (RLR), in the heavy chain, which is rapidly and stoichiometrically modified by trinitrobenzenesulfonate. Our previous kinetic study (Komatsu, H., Emoto, Y., and Tawada K. (1993) J. Biol. Chem. 268, 7799-7808) showed that although MgPPi reduces the maximum number of trinitrophenylated RLR down to about 0.5 mol/mol of S1, this half-stoichiometric modification of RLR is not the result of any heterogeneity in the primary structure of S1. However, this result conflicts with a previous report in which the half-stoichiometric trinitrophenylation has been reported to be related to Pro/Ser microheterogeneity at the 78th residue position in the heavy chain of rabbit skeletal muscle myosin. To resolve the conflict, we isolated peptides containing both the 78th residue and RLR from the two different preparations of S1, one whose RLR was trinitrophenylated in the presence of MgPPi and the other whose RLR was not trinitrophenylated in the presence of MgPPi, and then we determined the amino acid sequences of the peptides. We found the same Pro/Ser microheterogeneity at the 78th position in the peptides from these S1s and thus concluded that this microheterogeneity has no correlation to the half-stoichiometric trinitrophenylation of RLR.

Half-stoichiometric trinitrophenylation of myosin subfragment 1 in the presence of pyrophosphate or adenosine diphosphate

A molecule of myosin subfragment 1 (S1) from skeletal muscle has one reactive lysine residue (RLR) that is rapidly and stoichiometrically modified by trinitrobenzene sulfonate (TNBS). Previous studies on the RLR modification with TNBS in the presence of inorganic pyrophosphate (PPi) by others suggested the non-identical nature of the two myosin heads which is still controversial. To resolve this issue, we studied the effects of PPi and ADP on the trinitrophenylation reaction over a wide range of ligands more systematically, by using S1 containing the alkali 1 light chain. We herein show that MgPPi or MgADP reduces the maximum number of trinitrophenylated RLRs down to about 0.5 mol/mol of S1 and that this half-stoichiometric modification of RLRs is not the result of heterogeneity in the primary structure of S1. Instead, our results suggest the existence of two almost equimolar, different conformations of S1.PPi and S1.ADP. Furthermore, we show evidence that the two different conformations are in a slow equilibrium in the presence of TNBS. We also studied the effects of the stoichiometric and half-stoichiometric RLR modification on the EDTA- and Mg-ATPase activities of S1 and found no evidence for the functional heterogeneity of the myosin active site.

Dynamical role of "protein friction" in the sliding movement of protein motors in vitro

When protein motors interact with a sliding cytoplasmic-filament through a weak-binding interaction (thus, without ATP splitting), this interaction cycle results in friction opposing the sliding movement. The friction is owing to the flexible nature of the heads of these motors as globular proteins. Under a certain condition, the friction becomes proportional to the sliding velocity. This viscous-like friction by protein motor is called protein friction. Since the protein friction is more than 10 times larger than the hydrodynamic viscous drag, we propose that the sliding velocity in the in vitro motility system is limited when the active sliding force generated by protein motors is balanced by the protein friction. The model of the protein friction hypothesis is consistent with many experimental data of the in vitro motility systems such as those of mixture experiments with different myosins and the ATP-concentration dependence of the sliding velocity. By relating the coefficient of the protein friction to the diffusion coefficient, we show that the model is consistent with the data on the one-dimensional Brownian movement of a microtubule on a dynein-coated glass surface in the presence of vanadate and ATP. The model also shows that the Brownian movement is driven directly by the thermally-generated structural fluctuations of the dynein heads rather than the atomic collision of solvent molecules. Thus, the model implies that the thermal structural fluctuations of the protein motor heads underlie the ATP-induced sliding movement by protein motors and hence protein motors are a Brownian actuator.

Effects of ionic strength on force transients induced by flash photolysis of caged ATP in covalently crosslinked rabbit psoas muscle fibers

Single fibers from glycerinated rabbit psoas muscle were treated with 1-ethyl-3[3-(dimethylamino) propyl] carbodiimide (EDC), after rigor was induced, to crosslink myosin heads to actin. The optimally pre-stretched (approximately 1.8%), partially crosslinked fibers produce a large force when MgATP is depleted, and this force is abolished when MgATP is reintroduced, even in high ionic strength solution of 0.5 M (Tawada et al. 1989). We investigated the rate of force decay in the crosslinked, force-producing fibers using pulse photolysis of caged ATP (Goldman et al. 1984). The decay of force was fast, the rate of which depending both on the ionic strength and on the amount of ATP released (0.2-2.2 mM) with the second-order rate constant of 0.5-1 x 10(5) M-1s-1 at the ionic strength of 0.5 M. At high ionic strength (1-2M) force decayed at lower rate. At low ionic strength (0.1-0.2 M), however, force decayed more rapidly, but force redeveloped subsequently, which is probably caused by uncrosslinked myosin heads.

Cross-linking of contractile proteins from skeletal muscle by treatment with microbial transglutaminase

The action on muscle proteins of microbial transglutaminase (MTGase), which catalyzes the formation of a "zero-length" covalent cross-link between glutamine and lysine residues in peptides, was studied in order to define a basis for future application of MTGase cross-linking to the study of muscle protein interaction. We examined the cross-linking of skeletal muscle myosin, myosin subfragments, actin, and myofibrils by treatment with MTGase and the possible side-effects of the cross-linking on the enzymic activity of myosin, and found that the rod portions of myosin in myosin filaments were quickly cross-linked to each other by the action of MTGase, but myosin subfragment 1 was not cross-linked to actin. The MgATPase activities at 0.5 M KCl of myosin, heavy meromyosin, subfragment 1, and subfragment 1-actin were not significantly affected by the MTGase reaction. A very small fraction of the head portion of heavy meromyosin was cross-linked to actin in their rigor complexes by MTGase, and the ATPase activity at 0.5 M KCl of the cross-linked heavy meromyosin-actin complexes was slightly enhanced.

Protein friction exerted by motor enzymes through a weak-binding interaction

Recently Vale et al. (1989, Cell 59, 915-925.) reported an observation of the one-dimensional Brownian movement of microtubules bound to flagellar dynein through a weak-binding interaction. In this study, we propose a theoretical model of this phenomenon. Our model consists of a rigid microtubule associated with a number of elastic dynein heads through a weak-binding interaction at equilibrium. The model implies that (1) the Brownian motion of the microtubule is not directly driven by the atomic collision of the solvent particles, but is driven by the thermally-generated structural fluctuations of the dynein heads which interact with the microtubule; (2) dynein heads through a weak-binding interaction exert a frictional drag force on the sliding motion of the microtubule and the drag force is proportional to the sliding velocity the same as in hydrodynamic viscous friction. This protein friction, with such viscous-like characteristics, may well play a role as a velocity-limiting factor in the normal ATP-induced sliding movement of motile proteins.

A physical model of ATP-induced actin-myosin movement in vitro

The nature of the mechanism limiting the velocity of ATP-induced unidirectional movements of actin-myosin filaments in vitro is considered. In the sliding process two types of "cyclic" interactions between myosin heads and actin are involved, i.e., productive and nonproductive. In the productive interaction, myosin heads split ATP and generate a force which produces sliding between actin and myosin. In the nonproductive interaction "cycle," on the other hand, myosin heads rapidly attach to and detach from actin "reversibly," i.e., without splitting ATP or generating an active force. Such a nonproductive interaction "cycle" causes irreversible dissipation of sliding energy into heat, because the myosin cross-bridges during this interaction are passive elastic structures. This consideration has led us to postulate that such cross-bridges, in effect, exert viscous-like frictional drag on moving elements. Energetic considerations suggest that this frictional drag is much greater than the hydrodynamic viscous drag. We present a model in which the sliding velocity is limited by the balance between the force generated by myosin cross-bridges in the productive interaction and the frictional drag exerted by other myosin cross-bridges in the nonproductive interaction. The model is consistent with experimental findings of in vitro sliding, including the dependence of velocity on ATP concentration, as well as the sliding velocity of co-polymers of skeletal muscle myosin and phosphorylated and unphosphorylated smooth muscle myosins.

Covalent crosslinking of myosin subfragment-1 and heavy meromyosin to actin at various molar ratios: different correlations between ATPase activity and crosslinking extent

This paper describes a systematic study of crosslinking of skeletal muscle myosin subfragment-1 (S1) and heavy meromyosin (HMM) to F-actin in the rigor state with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC). We followed the time courses of S1 or HMM head crosslinking at various actin:S1 or actin:HMM head molar ratios and the resulting superactivation of ATPase activity. The ATPase activity of the covalent complexes was measured at 0.5 M KCl, where the covalent complexes retain superactivated ATPase activity but the activity of uncrosslinked myosin heads is not activated by actin. S1 crosslinking was slowest at the actin:S1 molar ratio of 1:1, but faster at larger molar ratios, where more than 80% of added S1 could be crosslinked to actin. In spite of the dependence of crosslinking rate on actin:S1 ratio, there were two linear correlations between ATPase activity and the extent of S1 crosslinking to actin: one for S1 crosslinked to actin at actin:S1 molar ratios more than 2.7:1 and the other for S1 crosslinked at a molar ratio of 1:1. Extrapolation of the former correlation line to 100% crosslinked S1 gave an ATPase activity of 39 s-1 for actin-S1 covalent complex at 25 degrees C, whereas that of the other correlation line gave 21 s-1. The latter smaller activity suggests that the interface between actin and S1 in their rigor complexes at a molar ratio of 1:1 is different from that at molar ratios of more than 2.7:1. The acto-HMM crosslinking rate depended on the ratio of actin to HMM head, like that of S1 crosslinking to actin. The ATPase activity of crosslinked actin-HMM was, unlike that of actin-S1 covalent complexes, bell-shaped as a function of the crosslinked heads, but chymotryptic conversion of HMM to S1 in the covalent complexes made the bell-shaped characteristics disappear and increased the activity close to that of actin-S1 covalent complexes. These results indicate that some physical constraint imposed on myosin heads suppresses the actin-activated ATPase activity of HMM crosslinked to actin.

Covalent cross-linking of single fibers from rabbit psoas increases oscillatory power

Single fibers from chemically skinned rabbit psoas muscle were treated with 1-ethyl-3-[3-dimethyl-amino)proyl]-carbodiimide (EDC) at 20 degrees C after rigor was induced. A 22-min treatment resulted in 18% covalent cross-linking between myosin heads and the thin filament as determined by stiffness measurements. This treatment also results in covalent cross-linking among rod portions of myosin molecules in the backbone of the thick filament. The fibers thus prepared are stable and do not dissolve in solutions at ionic strengths as high as 1,000 mM. The preparation was subjected to sinusoidal analysis, and the resulting complex modulus data were analyzed in terms of three exponential processes, (A), (B), and (C). Oscillatory work (process B) was much greater in the cross-linked fibers than in untreated ones in activating solutions of physiological ionic strength (200 mM); this difference was attributed to the decline of process (A) with EDC treatment. Consequently, the Nyquist plot of the EDC-treated preparation exhibited an insect-type response. We conclude that, under these conditions, both cross-linked and non-cross-linked myosin heads contribute to the production of oscillatory power. The cross-linked preparations also exhibited oscillatory work in high ionic strength (500-1,000 mM) solutions, indicating that cross-linked myosin heads are capable of utilizing ATP to produce work. We conclude that process (A) does not relate to an elementary step in a cross-bridge cycle, but it may relate to dynamics outside the cross-bridge such as filament sliding or sarcomere rearrangement.

Separation of SH-modified myosin subfragment-1 (A1) isozyme into two distinct equimolar fractions by an affinity chromatography

Our previous kinetic studies indicated that SH-modified myosin subfragment-1 A1 isozyme (S1(A1] contains at least two different types of active sites (Emoto, Y., Kawamura, T., & Tawada, K. (1985) J. Biochem. 98, 735-745). In those studies we have modified highly reactive SH-groups in S1(A1) with thimerosal. In this work, we separated the modified S1(A1) into two equimolar fractions by affinity chromatography with agarose-ADP. For the separation, Mg2+ in the elution buffer was indispensable. Although the two fractions appeared to have the same number of modified SH-groups per mol of S1, they had different enzymic and fluorescent properties. SH-modification with an excess of thimerosal for a much longer duration did not change any of the results: not the chromatographic profile, the properties of the two fractions, nor the number of modified SH-groups. Hence the two different populations were not generated by incomplete modification. After reduction with dithiothreitol, however, the differences between the two fractions disappeared. When we separately re-modified the reduced fractions and re-chromatographed them, in each case we again obtained two fractions, which had the same properties as the two fractions obtained from the original modification with thimerosal. These results demonstrate that the active site heterogeneity in SH-modified S1(A1) had no intrinsic origin in the unmodified S1: it was introduced by the SH-modification, but by an unknown mechanism(s) other than incomplete modification.

Stiffness of carbodiimide-crosslinked glycerinated muscle fibres in rigor and relaxing solutions at high salt concentrations

In this article, we have applied a crosslinking technique with a water-soluble carbodiimide to single glycerol-extracted muscle fibres from the rabbit. We have measured the stiffness of the fibres in a relaxing solution at high salt concentration. These fibres were crosslinked to varying extents in the rigor state. The relaxing solution caused uncrosslinked crossbridge heads (S1) to detach. High salt concentrations were used because the fibres were not activated by the crosslinked crossbridges under these conditions, although they were at physiological ionic strength. We found a linear correlation between the extent of S1 crosslinking to thin filaments and the stiffness and that the stiffness in the relaxing solution of muscle fibres with all the S1 heads crosslinked to thin filaments was the same as the rigor stiffness of the fibres before crosslinking. We conclude that the sarcomere compliance is mostly a property of the crossbridges (with more than 65% of the crossbridge compliance in the S1 portions and less than 35% in the S2 portion) and little of other sarcomere structures. In an earlier paper [Kimura & Tawada, Biophys. J. 45, 603-10 (1984)], we demonstrated that the S2 portion of the crossbridge was stiff. It then follows that the crossbridge compliance, and thus the sarcomere compliance, is a property of the S1 heads. Assuming that the S1 portion of the crossbridges in rigor strained muscle fibres is bent, we calculated the Young's modulus of the S1 portion and found that it is about 10(2) MN m-2. Because this order of magnitude is reasonable in terms of globular protein elasticity, bending is likely to be the nature of the S1 compliance in rigor muscle fibres.

Characterization of the ATPase active site in myosin subfragment-1 with the use of vanadate plus ADP as a reversible "affinity-labeling" reagent: evidence for heterogeneity in the active sites

Our previous work showed that the active site heterogeneity in heavy meromyosin (HMM) becomes evident when highly reactive SH-groups in HMM are modified by thimerosal (Kawamura, Higuchi, Emoto, & Tawada (1985) J. Biochem. 97, 1583-1593). The heterogeneity was revealed by "affinity-labeling" analysis with vanadate plus ADP, which was developed in the previous paper. To see whether this heterogeneity is due to the head-head interaction or two different alkali light chains present in HMM, we carried out similar studies with myosin subfragment-1 (S1) and one of the isozymes, S1(A1), which contains only the alkali light chain 1, and obtained essentially the same results as those previously obtained with HMM. The S1 results are easily explained by the same hypothesis previously used for explaining the HMM results: SH-modified S1 or S1(A1) contains two kinds of active site in a 1:1 ratio with almost the same ATPase activity: one hydrolyzes ATP by a mechanism giving a protein Trp fluorescence enhancement, whereas the other hydrolyzes ATP by another mechanism giving no fluorescence enhancement.

Relationship between the ATPase activity and the ATP-induced fluorescence enhancement of SH-modified heavy meromyosin during its fractional inactivation by vanadate plus ADP: evidence for heterogeneity in the active sites

We have examined whether heavy meromyosin (HMM) consists of a single kind of active site by analyzing the changes in the relative MgATPase activity and the relative amplitude of the ATP-induced fluorescence enhancement of the protein when the fraction of HMM "affinity"-labeled by vanadate plus ADP was varied. The analysis is based on a prediction that these two changes should be proportional to each other if myosin consists of a single kind of active site and generates the rate-limiting myosin**product complex emitting enhanced fluorescence. Although the difference between these two changes was very small with native HMM, it was large with HMM in which 5 fast-reactive sulfhydryl-groups per head were pre-modified with thimerosal. The difference indicated the existence of heterogeneous active sites in the SH-modified HMM. The results were best explained in terms of the hypothesis that fifty percent of the active site splits MgATP by a mechanism giving a fluorescence enhancement whereas the other fifty percent splits MgATP by another mechanism giving no fluorescence enhancement. Two possible explanations for the existence of heterogeneous active sites in the SH-modified HMM are discussed. One assumes the pre-existence of some sort of 1:1 heterogeneity in the micro-environment of the active sites and the other, which is considered less likely, assumes the introduction of the heterogeneity as a result of the SH-modification.

Is the SII portion of the cross-bridge in glycerinated rabbit psoas fibers compliant in the rigor state?

To see whether the SII portion of the cross-bridge in rigor fibers is longitudinally compliant, we chemically cross-linked with dimethyl suberimidate the entire rod portion (including the SII portion) of myosin onto the surface of thick filaments in glycerinated rabbit psoas fibers, and studied the effect of the SII fixation on the stiffness of the rigor fibers. The cross-linking of fiber segments with full filament overlap increased the rigor stiffness by approximately 25%. Almost the same absolute amount of the stiffness increase was also observed in rigor fibers with half- or no filament overlap after the cross-linking, and a similar but somewhat larger increment of stiffness was observed in fiber segments cross-linked in relaxing solution. These results indicate that the stiffness increase is not produced by the fixation of the SII portion onto the thick filament surface, but is caused instead by the cross-linking of some parallel elastic elements in muscle, and therefore indicate that the SII portion of the cross-bridge is hardly longitudinally compliant in rigor fibers.

Stiffness of glycerinated rabbit psoas fibers in the rigor state. Filament-overlap relation

The stiffness of glycerinated rabbit psoas fibers in the rigor state was measured at various sarcomere lengths in order to determine the distribution of the sarcomere compliance between the cross-bridge and other structures. The stiffness was determined by measuring the tension increment at one end of a fiber segment while stretching the other end of the fiber. The contribution of the end compliance to the rigor segments was checked both by laser diffractometry of the sarcomere length change and by measuring the length dependence of the Young's modulus; the contribution was found to be small. The stiffness in the rigor state was constant at sarcomere lengths of 2.4 microns or less; at greater sarcomere lengths the stiffness, when corrected for the contribution of resting stiffness, scaled with the amount of overlap between the thick and thin filaments. These results suggest that the source of the sarcomere compliance of the rigor fiber at the full overlapping of filaments is mostly the cross-bridge compliance.

Cross-linking studies related to the location of the rigor compliance in glycerinated rabbit psoas fibers: is the SII portion of the cross-bridge compliant?

The muscle tension generation model of Huxley and Simmons (1971) postulates an independent elastic element in the cross-bridge. This elastic structure was tentatively placed in the SII portion of the cross-bridge in the model. To check this assumption, we fixed the SII portion onto the surface of the thick filament in glycerinated rabbit psoas fibers in rigor by chemically cross-linking with dimethyl suberimidate, and compared the stiffness of the cross-linked fibers with that of the fibers before cross-linking. The stiffness was determined by measuring the tension increment upon stretching a fiber segment in rigor. The contribution of the end compliance was found to be small. Cross-linking increased the rigor stiffness by 20 to 30%. Almost the same amount of the stiffness increase was also observed at a sarcomere length where there was no overlap between the thin and thick filaments, and in a fiber segment cross-linked in relaxing solution. Therefore, the 20 to 30% increase of the stiffness is not caused by the fixation of the SII portion onto the thick filament but caused by the cross-linking of some parallel elastic components. Since the rigor stiffness before cross-linking is almost proportional to the overlap between thick and thin filaments, we conclude that the muscle stiffness in rigor does not originate in the SII portion but reflects some compliance of the head portion of the cross-bridge.

Dissociation of actomyosin by vanadate plus ADP, and decomposition of the myosin-ADP-vanadate complex by actin

In the presence of vanadate (Vi) and ADP, myosin ATPase forms a stable inactive complex (myosin.ADP.Vi) at the active site. To elucidate the nature of the inactive complex, we studied the effect of Vi plus ADP on the interaction of heavy meromyosin (HMM) with F-actin. 1) Viscosity measurements showed that the actin-HMM rigor complex was dissociated into actin and HMM by Vi and ADP (both 10(-3) M range). 2) When the HMM.ADP.Vi complex isolated by gel filtration was mixed with actin in the absence of free Vi, about 60% of the added HMM formed a complex with actin, and more than 70% of the HMM bound to actin released Vi and ADP. 3) When a mixture of the isolated HMM.ADP.Vi complex with actin was dialyzed against a buffer without free Vi and free ADP, only less than 10% of Vi and ADP, which were originally bound to the HMM, were retained in the dialysis tube after 4 days. In contrast, if actin was omitted, about 80% of Vi and ADP were retained. 4) These results indicate that the HMM.ADP-Vi complex is dissociated from actin, and that Vi and ADP originally trapped at the HMM active site can be almost completely released from the active site by actin if free (released) Vi and ADP are concomitantly removed.

Study of tropomyosin labelled with a fluorescent probe by pulse fluorimetry in polarized light. Interaction of that protein with troponin and actin

Tropomyosin has been labelled with a fluorescent probe N-iodoacetyl-N'-(5-sulfo-1-naphthyl)-ethylenediamine which is presumed to bind preferentially to the unique reactive cysteine residue of the alpha chain. Anisotropy decay measurements show that tropomyosin monomer and polymer are flexible molecules. This flexibility decreases when troponin interacts with tropomyosin, and is partially restored by a micromolar concentration of Ca2+.