Role of angiography in the detection of aortic branch vessel injury after blunt thoracic trauma

PURPOSE

The occurrence of aortic arch branch vessel injury as an isolated occurrence or in association with aortic injury after blunt chest trauma has not been emphasized in the literature. The imaging evaluation is also controversial.

METHODS

We reviewed thoracic aortograms of 166 patients examined at our institution from May 1995 to May 1999 performed after blunt thoracic trauma. We evaluated the aortograms for aortic and arch branch vessel injuries. Twenty-four injuries were detected and all patients had either a wide mediastinum demonstrated on plain radiographs (22 patients) or mechanism of injury conducive to aortic injury.

RESULTS

Of the 166 patients, 24 (14%; 16 men, 8 women; mean age, 50 years) had aortic or arch branch vessel injuries. Isolated aortic injury occurred in 15 (9%) of 166 patients. Branch vessel injury occurred in 9 (5%) of 166 patients; seven patients (10 branch vessels) had isolated branch vessel injury and two patients (three branch vessels) had branch vessel injury associated with aortic injury. The injured branch vessels were brachiocephalic artery (four), left common carotid artery (four), left subclavian artery (three), right internal mammary artery (one), and left vertebral artery (one). The types of branch vessel injuries included intimal tears (nine vessels; 69%), and transection causing a pseudoaneurysm (four vessels; 31%). Revised Trauma Scores in patients with branch vessel injuries were 12 in seven patients and 11 and 4 in one each.

CONCLUSION

We emphasize the angiographic findings in these patients that can at times be quite subtle. Awareness of the incidence of such injuries either in isolation or associated with aortic injury has implications regarding evaluation of this patient population with less invasive techniques such as CT or transesophageal echocardiography.

Mutant protein in Huntington disease is resistant to proteolysis in affected brain

The cause of Huntington disease pathophysiology is unknown, but a major hypothesis suggests that toxicity arises from the cleavage and accumulation of amino-terminal fragments containing an expanded polyglutamine region. In evaluating huntingtin protein (HD) from human brain, transgenic animals and cells, we observed, unexpectedly, that mutant HD is more resistant to proteolysis than normal HD. The N-terminal cleavage fragments we observed arise from the processing of normal HD and are sequestered by full-length mutant HD. Our results support a model in which inhibition of proteolysis of mutant HD leads to aggregation and toxicity through the sequestering of important targets, including normal HD.

There is communication between all four Ca(2+)-bindings sites of calcineurin B

We have used site-directed mutagenesis, flow dialysis, and Fourier transform infrared (FTIR) spectroscopy to study Ca(2+)-binding to the regulatory component of calcineurin. Single Glu-Gln(E --> Q) mutations were used to inactivate each of the four Ca(2+)-binding sites of CnB in turn, generating mutants Q1, Q2, Q3, and Q4, with the number indicating which Ca(2+) site is inactivated. The binding data derived from flow dialysis reveal two pairs of sites in the wild-type protein, one pair with very high affinity and the other with lower affinity Ca(2+)-binding sites. Also, only three sites are titratable in the wild-type protein because one site cannot be decalcified. Mutation of site 2 leaves the protein with only two titratable sites, while mutation of sites 1, 3, or 4 leave three titratable sites that are mostly filled with 3 Ca(2+) equiv added. The binding data further show that each of the single-site mutations Q2, Q3, and Q4 affects the affinities of at least one of the remaining sites. Mutation in either of sites 3 or 4 results in a protein with no high-affinity sites, indicating communication between the two high-affinity sites, most likely sites 3 and 4. Mutation in site 2 decreases the affinity of all three remaining sites, though still leaving two relatively high-affinity sites. The FTIR data support the conclusions from the binding data with respect to the number of titratable sites as well as the impact of each mutation on the affinities of the remaining sites. We conclude therefore that there is communication between all four Ca(2+)-binding sites. In addition, the Ca(2+) induced changes in the FTIR spectra for the wild-type and Q4 mutant are most similar, suggesting that the same three Ca(2+)-binding sites are being titrated, i.e., site 4 is the very high-affinity site under the conditions of the FTIR experiments.

Structures of apomyoglobin's various acid-destabilized forms

The structures and the cold and hot melting thermodynamics of the acid- and salt-destabilized states of horse heart apomyoglobin (apoMb), including the E (extended) and various I forms, are studied using probes of tertiary structure (tryptophan fluorescence and FTIR spectroscopy) and secondary structure (far-UV CD and FTIR spectroscopy). These forms likely resemble early structures in the folding of the largely helical protein. Both the I and E forms retain the AGH core whereby the two ends of the protein are tied together with sufficient numbers of tertiary contacts, involving a number of hydrophobic residues, to show cooperative melting. The melting thermodynamics of E and I are distinctly different. E contains no other tertiary structure and probably little other secondary structure apart from the core. The more destabilized E form appears to contain "random" buried runs of polypeptide backbone which convert to alpha-helix in the I form(s). Most interestingly, E consists not of a single structure but is composed of a heterogeneous mixture of conformations, all showing corelike cooperative melting characteristics, and consisting presumably of varying contacts between the A portion of apomyoglobin and the G-H hairpin. These results bear on the energy landscape and structural features of the early part of apomyoglobin's folding pathway.

Core formation in apomyoglobin: probing the upper reaches of the folding energy landscape

An acid-destabilized form of apomyoglobin, the so-called E state, consists of a set of heterogeneous structures that are all characterized by a stable hydrophobic core composed of 30-40 residues at the intersection of the A, G, and H helices of the protein, with little other secondary structure and no other tertiary structure. Relaxation kinetics studies were carried out to characterize the dynamics of core melting and formation in this protein. The unfolding and/or refolding response is induced by a laser-induced temperature jump between the folded and unfolded forms of E, and structural changes are monitored using the infrared amide I' absorbance at 1648-1651 cm(-1) that reports on the formation of solvent-protected, native-like helix in the core and by fluorescence emission changes from apomyoglobin's Trp14, a measure of burial of the indole group of this residue. The fluorescence kinetics data are monoexponential with a relaxation time of 14 micros. However, infrared kinetics data are best fit to a biexponential function with relaxation times of 14 and 59 micros. These relaxation times are very fast, close to the limits placed on folding reactions by diffusion. The 14 micros relaxation time is weakly temperature dependent and thus represents a pathway that is energetically downhill. The appearance of this relaxation time in both the fluorescence and infrared measurements indicates that this folding event proceeds by a concomitant formation of compact secondary and tertiary structures. The 59 micros relaxation time is much more strongly temperature dependent and has no fluorescence counterpart, indicating an activated process with a large energy barrier wherein nonspecific hydrophobic interactions between helix A and the G and H helices cause some helix burial but Trp14 remains solvent exposed. These results are best fit by a multiple-pathway kinetic model when U collapses to form the various folded core structures of E. Thus, the results suggest very robust dynamics for core formation involving multiple folding pathways and provide significant insight into the primary processes of protein folding.

A photolysis-triggered heme ligand switch in H93G myoglobin

Resonance Raman spectroscopy and step-scan Fourier transform infrared (FTIR) spectroscopy have been used to identify the ligation state of ferrous heme iron for the H93G proximal cavity mutant of myoglobin in the absence of exogenous ligand on the proximal side. Preparation of the H93G mutant of myoglobin has been previously reported for a variety of axial ligands to the heme iron (e.g., substituted pyridines and imidazoles) [DePillis, G., Decatur, S. M., Barrick, D., and Boxer, S. G. (1994) J. Am. Chem. Soc. 116, 6981-6982]. The present study examines the ligation states of heme in preparations of the H93G myoglobin with no exogenous ligand. In the deoxy form of H93G, resonance Raman spectroscopic evidence shows water to be the axial (fifth) ligand to the deoxy heme iron. Analysis of the infrared C-O and Raman Fe-C stretching frequencies for the CO adduct indicates that it is six-coordinate with a histidine trans ligand. Following photolysis of CO, a time-dependent change in ligation is evident in both step-scan FTIR and saturation resonance Raman spectra, leading to the conclusion that a conformationally driven ligand switch exists in the H93G protein. In the absence of exogenous nitrogenous ligands, the CO trans effect stabilizes endogenous histidine ligation, while conformational strain favors the dissociation of histidine following photolysis of CO. The replacement of histidine by water in the five-coordinate complex is estimated to occur in < 5 micros. The results demonstrate that the H93G myoglobin cavity mutant has potential utility as a model system for studying the conformational energetics of ligand switching in heme proteins such as those observed in nitrite reductase, guanylyl cyclase, and possibly cytochrome c oxidase.

Human flap endonuclease-1: conformational change upon binding to the flap DNA substrate and location of the Mg2+ binding site

Human flap endonuclease-1 (FEN-1) is a member of the structure-specific endonuclease family and is a key enzyme in DNA replication and repair. FEN-1 recognizes the 5'-flap DNA structure and cleaves it, a specialized endonuclease function essential for the processing of Okazaki fragments during DNA replication and for the repair of 5'-end single-stranded tails from nicked double-stranded DNA substrates. Magnesium is a cofactor required for nuclease activity. We have used Fourier transform infrared (FTIR) spectroscopy to better understand how Mg2+ and flap DNA interact with human FEN-1. FTIR spectroscopy provides three fundamentally new insights into the structural changes induced by the interaction of FEN-1 with substrate DNA and Mg2+. First, FTIR difference spectra in the amide I vibrational band (1600-1700 cm(-1)) reveal a change in the secondary structure of FEN-1 induced by substrate DNA binding. Quantitative analysis of the FTIR spectra indicates a 4% increase in helicity upon DNA binding or about 14 residues converted from disordered to helical conformations. The observation that the residues are disordered without DNA strongly implicates the flexible loop region. The conversion to helix also suggests a mechanism for locking the flexible loop region around the bound DNA. This is the first direct experimental evidence for a binding mechanism that involves a secondary structural change of the protein. Second, in contrast with DNA binding, no change is observed in the secondary structure of FEN-1 upon Mg2+ binding to the wild type or to the noncleaving D181A mutant. Third, the FTIR results provide direct evidence (via the carboxylate ligand band at 1535 cm(-1)) that not only is D181 a ligand to Mg2+ in the human enzyme but Mg2+ binding does not occur in the D181A mutant which lacks this ligand.

Protein folding and unfolding on a complex energy landscape

Recent theories of protein folding suggest that individual proteins within a large ensemble may follow different routes in conformation space from the unfolded state toward the native state and vice versa. Herein, we introduce a new type of kinetics experiment that shows how different unfolding pathways can be selected by varying the initial reaction conditions. The relaxation kinetics of the major cold shock protein of Escherichia coli (CspA) in response to a laser-induced temperature jump are exponential for small temperature jumps, indicative of folding through a two-state mechanism. However, for larger jumps, the kinetics become strongly nonexponential, implying the existence of multiple unfolding pathways. We provide evidence that both unfolding across an energy barrier and diffusive downhill unfolding can occur simultaneously in the same ensemble and provide the experimental requirements for these to be observed.

CT diagnosis of acute flank pain from urolithiasis

The use of noncontrast helical CT (NHCT) to assess patients with acute flank pain and hematuria for potential urinary tract stone disease was first reported in 1995. After several years of experience with the technique, sensitivity and specificity of NHCT has proven to be better than intravenous urography for evaluating ureteral stones. NHCT imaging findings for urinary calculi and the differential diagnosis are discussed in this article. Various extraurinary diseases found while using NHCT in searching for stone disease are addressed and illustrated. As experience with the use of NHCT has increased, clinicians have broadened the indications for this technique, which has a lower charge than standard CT, beyond the specific evaluation of urinary colic. This indication creep has increased the number of NHCT examinations ordered. It has also reduced the rate of stone positivity and increased the diagnostic yield for extraurinary disease.

Trends in the use of unenhanced helical CT for acute urinary colic

OBJECTIVE

Unenhanced helical CT for urolithiasis detection is a limited CT examination that was designed specifically for the detection of urolithiasis. The purpose of this study was to repeat a prior study to assess whether clinicians had broadened the indications and changed the yield and findings of unenhanced helical CT.

MATERIALS AND METHODS

One hundred consecutive patients with suspected renal colic or flank pain referred for unenhanced helical CT were selected for this study. We reviewed the original radiographic reports for each patient and recorded the presence of ureteral calculi. Other urinary abnormalities and extraurinary lesions were also recorded and compared with the results of the previous study.

RESULTS

In this study, 56% of the patients who underwent unenhanced helical CT had symptoms of urinary colic, and 44% of patients had unspecified flank pain, compared with 100% of patients with symptoms of urinary colic 1 year earlier. The sensitivity and specificity of unenhanced helical CT in detecting ureteral calculi were 96% and 99%, respectively. Ureteral calculi were identified in only 28% of the patients versus 49% of patients (p < .01) 1 year earlier. Extraurinary lesions were identified in 45% of the patients versus 16% (p < .01) 1 year before.

CONCLUSION

As clinicians developed familiarity with this technique, the indications for performance of unenhanced helical CT were expanded with a consequent reduction in the rate of detection of stone disease and identification of an increased number of extraurinary lesions, which suggests a demand for emergency abdominal CT studies.

Abnormal calcification on plain radiographs of the abdomen

The purpose of this pictorial review is to facilitate recognition and understanding of calcifications seen on conventional radiographs of the abdomen. Calcifications can be categorized by organ system and location in the abdomen. Both common and rare calcifications in the urinary tract, liver, gallbladder, spleen, pancreas, adrenal glands, digestive tract, genital tract, peritoneal cavity, and retroperitoneum are illustrated. Abnormal calcifications in the urinary tract are subcategorized by kidneys, ureters, bladder, and urethra. The density, shape, size, margins, pattern, position, and mobility of calcifications are emphasized for differential diagnoses.

Do's and don't's of percutaneous nephrostomy

Percutaneous nephrostomy procedures generally are safe. The associated mortality rate is approximately 0.04%, and the incidence of important complications is 5% (2-4). To minimize complications, certain precautions always should be followed. First, radiologists should perform a preprocedural evaluation of the patient, with correction of marked coagulopathy or thrombocytopenia before all but the most emergent procedures. Second, antibiotics should be administered routinely before nephrostomy drainage; the choice of antibiotics can be based on the specific patient's risk factors for bacteriuria. To minimize the risk of clinically important renal vascular damage, radiologists should do the following: 1. Always achieve adequate visualization of the calices. 2. Identify a posterior calix for puncture that will give access to the appropriate segment of the kidney for anticipated procedures and allow safe creation of a tract. 3. Puncture below the 11th rib (and preferably below the 12th rib when feasible). 4. Puncture the tip of a posterior calix from a 20 degrees-30 degrees, posterolateral oblique approach to avoid major blood vessels. 5. Make a single-wall puncture of the calix. 6. Perform exchange transfusion for opacification of the renal pelvis and calices during percutaneous nephrostomy procedures to minimize the risk of sepsis. Overdistention can increase the likelihood of sepsis or retroperitoneal contamination. 7. Inject contrast material via a catheter placed over a wire to confirm the intracollecting system location of the entry. 8. Avoid unnecessary (complicated, prolonged) procedures in an infected, obstructed system. 9. Use only self-retaining drainage catheters to minimize the risk of inadvertent catheter dislodgment. 10. Create large-bore tracts with a balloon dilation system. By contrast, radiologists should not do the following: 1. Puncture above the 11th rib (unless all other avenues of approach have been exhausted). 2. Lose access to an obstructed kidney once the kidney has been punctured. Placement of a "safety" wire for all complex manipulations is recommended. 3. Panic if excessive bleeding or evidence of adjacent organ injury is seen. Excessive bleeding usually can be stopped with tract tamponade by using a balloon catheter advanced through the tract or with placement of an appropriate-sized nephrostomy tube to occlude the tract. If active bleeding continues or recurs, arteriography should be considered. The quantity of bleeding can be monitored with sequential hematocrit measurements. Almost all renal artery injuries can be treated with minimally invasive procedures, such as selective embolization of the branch artery involved, and this will lead to infarction of only a small segment of kidney, with preservation of functioning renal parenchyma. Injury to an adjacent organ usually can be treated nonsurgically (21,23). The most commonly injured extrarenal abdominal organ is the colon (Fig 6). On occasion, a percutaneous nephrostomy needle may traverse the retroperitoneal segment of the colon, and this type of injury generally can be treated nonsurgically, as well (23). If the colon has been traversed, adequate urinary drainage should be ensured before the transcolonic nephrostomy catheter is removed (so that a nephrocolonic fistula is not maintained). This can be done by placing a ureteral stent and a bladder catheter (18). Once adequate urinary drainage is provided, the nephrostomy catheter can be withdrawn into the colon and used as a percutaneous colostomy drain. The percutaneous colostomy tract should be allowed to mature for several days before this catheter is removed. In addition, appropriate antibiotics should be administered from the time a transcolonic tract is identified until the percutaneous tract has healed completely. Transthoracic entry can cause pneumothorax and pleural effusions. These should be treated only if they are large or cause symptoms (21). (ABSTRACT TRUNCATED)

Fast events in protein folding: the time evolution of primary processes

Most experimental studies on the dynamics of protein folding have been confined to timescales of 1 ms and longer. Yet it is obvious that many phenomena that are obligatory elements of the folding process occur on much faster timescales. For example, it is also now clear that the formation of secondary and tertiary structures can occur on nanosecond and microsecond times, respectively. Although fast events are essential to, and sometimes dominate, the overall folding process, with a few exceptions their experimental study has become possible only recently with the development of appropriate techniques. This review discusses new approaches that are capable of initiating and monitoring the fast events in protein folding with temporal resolution down to picoseconds. The first important results from those techniques, which have been obtained for the folding of some globular proteins and polypeptide models, are also discussed.

Abnormal calcifications in the urinary tract

A wide variety of calcifications may develop in the urinary tract. Calculi, the most common form of urinary tract calcification, are usually radiopaque due to their calcium content, whereas cystine stones tend to be less opaque. In cortical nephrocalcinosis, calcification may be spotty or may appear as a thin rim outlining the cortex. Intracystic calcification is usually thin and peripheral and is often described as having an "eggshell" appearance. In renal masses, pure central calcification usually indicates malignancy, although malignancy may also be present with pure peripheral calcification. An incomplete ring of calcification seen over the central portion of the kidney should suggest the presence of an abnormal vascular structure. A sloughed papilla may lead to calcification that is usually triangular or ring-shaped or has a broken rim pattern. Ureteral calculi usually have a uniform radiopacity, whereas phleboliths are often less opaque centrally. Like renal calculi, bladder calculi usually contain a calcium component; they may be laminated, faceted, spiculated, or seedlike in appearance. Urachal carcinoma is commonly associated with tumor calcification, which typically occurs at the dome of the bladder. Schistosomiasis of the bladder may produce mural calcification with a typical thin arcuate pattern and may be associated with calcification in other portions of the urinary tract. Although urinary tract calcifications may be difficult to characterize specifically, they can be classified according to location, appearance, and relation to various pathologic conditions.

The core of apomyoglobin E-form folds at the diffusion limit

The E-form of apomyoglobin has been characterized using infrared and fluorescence spectroscopies, revealing a compact core with native like contacts, most probably consisting of 15-20 residues of the A, G and H helices of apomyoglobin. Fast temperature-jump, time-resolved infrared measurements reveal that the core is formed within 96 micros at 46 degrees C, close to the diffusion limit for loop formation. Remarkably, the folding pathway of the E-form is such that the formation of a limited number of native-like contacts is not rate limiting, or that the contacts form on the same time scale expected for diffusion controlled loop formation.

Cyanide binding and active site structure in heme-copper oxidases: normal coordinate analysis of iron-cyanide vibrations of a3(2+)CN- complexes of cytochromes ba3 and aa3

The cyanide isotope-sensitive low-frequency vibrations of ferrous cyano complexes of cytochrome a3 are studied for cytochrome ba3 from Thermus thermophilus and cytochrome aa3 from bovine heart. Cyanide complexes of ba3 display three isotope sensitive frequencies at 512, 485, and 473 cm-1. The first is primarily an Fe-C stretching motion, whereas the lower wavenumber modes are bending motions. These iron-cyanide vibrations are independent of the redox levels of the other metal centers in the protein. On the other hand, the fully reduced bovine derivative complexed with cyanide gives rise to a bending vibration at 503 cm-1 and a stretching vibration at 469 cm-1. That is, the ordering of the stretching and bending frequencies is reversed from that of the bacterial protein. These results are analyzed by normal coordinate calculations to obtain comparative models for the binuclear O2 reducing site of the two proteins. We find that the observed frequencies are consistent with a linear Fe-C-N group and larger Fe-C stretching force constant (2.558 mdyn/A) for ba3 and a slightly bent Fe-C-N group (angle approximately 170 degrees) and a smaller Fe-C stretching force constant (2.335 mdyn/A) for aa3. Thus, there are significant differences in the interaction of cyanide with ferrous a3 in the two proteins that are most likely caused by a weaker proximal histidine interaction and stronger peripheral heme electron withdrawing effects in ba3. Possible sources of these protein-induced effects are discussed. Using the analysis developed here, comparison of the FeCN stretching and bending frequencies of the ferrous bovine a3-CN complex to those obtained from the ferric a3-CN complex suggests that upon conversion of the resting to the fully reduced protein, a conformational change occurs that constrains the ligand binding site.

GAA instability in Friedreich's Ataxia shares a common, DNA-directed and intraallelic mechanism with other trinucleotide diseases

We show that GAA instability in Friedreich's Ataxia is a DNA-directed mutation caused by improper DNA structure at the repeat region. Unlike CAG or CGG repeats, which form hairpins, GAA repeats form a YRY triple helix containing non-Watson-Crick pairs. As with hairpins, triplex mediates intergenerational instability in 96% of transmissions. In families with Friedreich's Ataxia, the only recessive trinucleotide disease, GAA instability is not a function of the number of long alleles, ruling out homologous recombination or gene conversion as a major mechanism. The similarity of mutation pattern among triple repeat-related diseases indicates that all trinucleotide instability occurs by a common, intraallelic mechanism that depends on DNA structure. Secondary structure mediates instability by creating strong polymerase pause sites at or within the repeats, facilitating slippage or sister chromatid exchange.

Fast events in protein folding: relaxation dynamics and structure of the I form of apomyoglobin

The fast relaxation dynamics of the acid destabilized I form of apomyoglobin (pH* 3, 0.15 M NaCl; apoMb-I) following a laser-induced temperature-jump have been probed using time-resolved infrared spectroscopy. Only a fast, single exponential phase is observed (bleach centered at v = 1633 cm-1 and transient absorbance at 1666 cm-1) with relaxation times of 38 ns at 30 degrees C and 36 ns at 57 degrees C; no additional slow (microsecond) phase is observed as previously found in the native form of apomyoglobin. Folding times of approximately 66 ns are derived from the observed rates based on a simple two-state model. The equilibrium melting of the 1633 cm-1 component shows noncooperative linear behavior over the temperature range studied (10-60 degrees C). The low amide I' frequency, the fast relaxation dynamics, and the noncooperative melting behavior are characteristic of isolated solvated helix. The analysis of the amide-I' band reveals another major component at 1650 cm-1 assigned to native-like structure stabilized by tertiary contacts involving the AGH core, which does not show dynamic or static melting under our conditions. ApoMb-I has generally been taken to be a "molten globule" species. The present results indicate a heterogeneous structure consisting of separate regions of native-like unit(s), solvated helices, and disordered coil, excluding a homogeneous molten globule as a model for apoMb-I. From the current studies and other results, a detailed model of the folding of apomyoglobin is presented.

Kinase-independent potentiation of B cell antigen receptor-mediated signal transduction by the protein tyrosine kinase Src

Signal transduction mediated by the B cell Ag receptor involves the activation of multiple protein tyrosine kinases that are members of the Src family (i.e., Fyn, Lyn, Blk, Lck). To determine whether members of the Src family possess common physical and/or enzymatic properties that enable them to potentiate signal transduction via the B cell Ag receptor, we expressed the protein tyrosine kinase Src in the B lymphoma cell line K46-17 mu m lambda. Based on coprecipitation analysis and two-color immunofluorescence, this heterologous Src family kinase was observed to physically associate with the B cell Ag receptor. Additional experiments demonstrated that B cell Ag receptor cross-linking results in increased tyrosine phosphorylation and activation of Src. Several parameters of B cell activation, including tyrosine phosphorylation of intracellular substrates, calcium mobilization, and transcription factor activation, were potentiated in cells that expressed Src when compared with control cells. To determine whether potentiation of Ag receptor-mediated signaling by Src was dependent on its catalytic activity, a kinase-deficient form of Src was expressed in K46-17 mu m lambda cells. Transfectants expressing kinase-deficient Src exhibited an enhanced responsiveness to stimulation through the B cell Ag receptor that was comparable with transfectants expressing wild-type Src. Additionally, kinase-deficient Src was observed to associate with the endogenous kinase Lyn in an activation-dependent manner. These findings indicate that members of the Src family may potentiate Ag receptor-mediated signaling via a kinase-independent mechanism(s) that involves amplification of kinase recruitment to the Ag receptor activation complex.

Kinase-independent potentiation of B cell antigen receptor-mediated signal transduction by the protein tyrosine kinase Src

Signal transduction mediated by the B cell Ag receptor involves the activation of multiple protein tyrosine kinases that are members of the Src family (i.e., Fyn, Lyn, Blk, Lck). To determine whether members of the Src family possess common physical and/or enzymatic properties that enable them to potentiate signal transduction via the B cell Ag receptor, we expressed the protein tyrosine kinase Src in the B lymphoma cell line K46-17 mu m lambda. Based on coprecipitation analysis and two-color immunofluorescence, this heterologous Src family kinase was observed to physically associate with the B cell Ag receptor. Additional experiments demonstrated that B cell Ag receptor cross-linking results in increased tyrosine phosphorylation and activation of Src. Several parameters of B cell activation, including tyrosine phosphorylation of intracellular substrates, calcium mobilization, and transcription factor activation, were potentiated in cells that expressed Src when compared with control cells. To determine whether potentiation of Ag receptor-mediated signaling by Src was dependent on its catalytic activity, a kinase-deficient form of Src was expressed in K46-17 mu m lambda cells. Transfectants expressing kinase-deficient Src exhibited an enhanced responsiveness to stimulation through the B cell Ag receptor that was comparable with transfectants expressing wild-type Src. Additionally, kinase-deficient Src was observed to associate with the endogenous kinase Lyn in an activation-dependent manner. These findings indicate that members of the Src family may potentiate Ag receptor-mediated signaling via a kinase-independent mechanism(s) that involves amplification of kinase recruitment to the Ag receptor activation complex.

Fourier transform infrared evidence for connectivity between CuB and glutamic acid 286 in cytochrome bo3 from Escherichia coli

Photodissociation of fully reduced, carbonmonoxy cytochrome bo3 causes ultrafast transfer of carbon monoxide (C triple bond O) from heme iron to CuB in the binuclear site. At low temperatures, the C triple bond O remains bound to CuB for extended times. Here, we show that the binding of C triple bond O to CuB perturbs the IR stretch of an un-ionized carboxylic acid residue, which is identified as Glu286 by mutation to Asp or to Cys. Before photodissociation, the carbonyl (C=O)-stretching frequency of this carboxylic acid residue is 1726 cm-1 for Glu286 and 1759 cm-1 for Glu286Asp. These frequencies are definitive evidence for un-ionized R-COOH and suggest that the carboxylic acids are hydrogen-bonded, though more extensively in Glu286. In Glu286Cys, this IR feature is lost altogether. We ascribe the frequency shifts in the C=O IR absorptions to the effects of binding photodissociated C triple bond O to CuB, which are relay ed to the 286 locus. Conversely, the 2065 cm-1 C triple bond O stretch of CuB-CO is markedly affected by both mutations. These effects are ascribed to changes in the Lewis acidity of CuB, or to displacement of a CuB histidine ligand by C triple bond O. C triple bond O binding to CuB also induces a downshift of an IR band which can be attributed to an aromatic C-H stretch, possibly of histidine imidazole, at about 3140 cm-1. The results suggest an easily polarizable, through-bond connectivity between one of the histidine CuB ligands and the carboxylic group of Glu286. A chain of bound water molecules may provide such a connection, which is of interest in the context of the proton pump mechanism of the heme-copper oxidases.

Structural heterogeneity of the various forms of apomyoglobin: implications for protein folding

Temperature-induced denaturation transitions of different structural forms of apomyoglobin were studied monitoring intrinsic tryptophan fluorescence. It was found that the tryptophans are effectively screened from solvent both in native and acid forms throughout most of the temperature range tested. Thus, the tryptophans' surrounding do not show a considerable change in structure where major protein conformational transitions have been found in apomyoglobin using other techniques. At high temperatures and under strong destabilizing conditions, the tryptophans' fluorescence parameters show sigmoidal thermal denaturation. These results, combined with previous studies, show that the structure of this protein is heterogeneous, including native-like (tightly packed) and molten globule-like substructures that exhibit conformation (denaturation) transitions under different conditions of pH and temperature (and denaturants). The results suggest that the folding of this protein proceeds via two "nucleation" events whereby native-like contacts are formed. One of these events, which involves AGH "core" formation, appears to occur very early in the folding process, even before significant hydrophobic collapse in the rest of the protein molecule. From the current studies and other results, a rather detailed picture of the folding of myoglobin is presented, on the level of specific structures and their thermodynamical properties as well as formation kinetics.

Bound water in the proton translocation mechanism of the haem-copper oxidases

We address the molecular mechanism by which the haem-copper oxidases translocate protons. Reduction of O2 to water takes place at a haem iron-copper (CuB) centre, and protons enter from one side of the membrane through a 'channel' structure in the enzyme. Statistical-mechanical calculations predict bound water molecules within this channel, and mutagenesis experiments show that breaking this water structure impedes proton translocation. Hydrogen-bonded water molecules connect the channel further via a conserved glutamic acid residue to a histidine ligand of CuB. The glutamic acid side chain may have to move during proton transfer because proton translocation is abolished if it is forced to interact with a nearby lysine or arginine. Perturbing the CuB ligand structure shifts an infrared mode that may be ascribed to the O-H stretch of bound water. This is sensitive to mutations of the glutamic acid, supporting its connectivity to the histidine. These results suggest key roles of bound water, the glutamic acid and the histidine copper ligand in the mechanism of proton translocation.

Update on interventional uroradiology

From its humble beginnings as a method of expediently decompressing the obstructed kidney, the field of interventional uroradiology has evolved in the hands of urologists and interventional radiologists to a means of addressing myriad problems in the urinary tract and has changed the day-to-day practice of urology. The foundation of interventional uroradiology is the creation of an appropriate entry into the urinary system. After a review of this basic procedure, extensions of the technique and new applications of emerging technology are reviewed.

Percutaneous transcatheter renal ablation with absolute ethanol for uncontrolled hypertension or nephrotic syndrome: results in 11 patients with end-stage renal disease

PURPOSE

Retrospective review of authors' experience with percutaneous transcatheter renal ablation in patients with uncontrolled hypertension and/or nephrotic syndrome.

MATERIALS AND METHODS

Between April 1987 and September 1995, renal ablation was performed on 11 patients aged 10 months to 21 years. All patients had end-stage renal disease (ESRD) with uncontrolled hypertension (10 patients) and/or nephrotic syndrome (four patients). Uncontrolled hypertension was defined as diastolic pressure greater than 90 mm Hg despite multidrug antihypertensive therapy. Nephrotic syndrome was defined as proteinuria exceeding 960 mg/m2 per day, serum albumin level less than 3 g/dL, and generalized edema. Embolization was performed with absolute ethanol from a common femoral artery approach. In most cases, a balloon catheter was used to prevent alcohol reflux into the aorta or nontarget renal artery branches, such as the adrenal arteries. Angiographic stasis of contrast material in the renal arteries was the endpoint.

RESULTS

All patients experienced a postembolization syndrome of 3-5 days duration, clinically manifested by variable degrees of nausea, vomiting, fever, and pain. Long-term improvement in hypertension was observed in nine patients. Improvement in hypertension was defined as diastolic blood pressure below 90 mm Hg while the patient received the same or fewer antihypertensive medications. The four patients with nephrotic syndrome were cured of their proteinuria and edema.

CONCLUSIONS

Transarterial renal ablation with alcohol is efficacious for treatment of uncontrolled hypertension and nephrotic syndrome in patients with ESRD. The morbidity and mortality in our series were less than those reported for surgical nephrectomy.

Radiologic findings in acute urinary tract obstruction

Acute urinary tract obstruction, a common disease in daily practice, often requires performance of emergency intravenous urography (IVU). However, the spectrum of urographic abnormalities seen with acute obstruction has not been thoroughly addressed. The purpose of this study was to explore the IVU findings in patients with acute urinary tract obstruction. Records of 380 patients who underwent IVU in our hospital during a 6-mo period were reviewed for IVU evidence of acute urinary tract obstruction. Of the 380 patients, 53 (14%; 39 men, 14 women; average age = 43 yr) had acute urinary tract obstruction. All obstructions except one were located in the lower one-third of the ureter. The causes of acute urinary obstruction included ureteral stones in 34 (64%), ureteral edema or lucent stones in 16 (30%), neoplasms in 2 (4%), and inflammatory disease in 1 (2%). Abnormal radiologic findings were hydroureter in 46, nephropyelographic delay in 36, hydronephrosis in 35, interureteric ridge edema in 11, persistent dense nephrogram in 6, urine extravasation in 5, vicarious excretion in 1, striation in 1, and stricture in 1. Radiographic results were normal in one patient. The most common clinical indications of acute ureteral obstruction are flank pain and hematuria, and calculi are the major cause. In one-third of patients, radiopaque calculi are not detectable with IVU during acute urinary tract obstruction. A careful and thorough evaluation of the IVU should be performed in patients with clinical indications of acute urinary obstruction.

Fast events in protein folding: relaxation dynamics of secondary and tertiary structure in native apomyoglobin

We report the fast relaxation dynamics of "native" apomyoglobin (pH 5.3) following a 10-ns, laser-induced temperature jump. The structural dynamics are probed using time-resolved infrared spectroscopy. The infrared kinetics monitored within the amide I absorbance of the polypeptide backbone exhibit two distinct relaxation phases which have different spectral signatures and occur on very different time scales (nu = 1633 cm(-1),tau = 48 ns; nu = 1650 cm(-1),tau = 132 micros). We assign these two spectral components to discrete substructures in the protein: helical structure that is solvated (1633 cm(-1)) and native helix that is protected from solvation by interhelix tertiary interactions (1650 cm(-1)). Folding rate coefficients inferred from the observed relaxations at 60 degrees C are k(f)(solvated) = (7 to 20) x 10(6) s(-1) and k(f)(native) = 3.6 x 10(3) s(-1), respectively. The faster rate is interpreted as the intrinsic rate of solvated helix formation, whereas the slower rate is interpreted as the rate of formation of tertiary contacts that determine a native helix. Thus, at 60 degrees C helix formation precedes the formation of tertiary structure by over three orders of magnitude in this protein. Furthermore, the distinct thermodynamics and kinetics observed for the apomyoglobin substructures suggest that they fold independently, or quasi-independently. The observation of inhomogeneous folding for apomyoglobin is remarkable, given the relatively small size and structural simplicity of this protein.

Locating the kidneys on CT to guide nephrotomography

Tomography of the kidneys is a routine procedure performed during intravenous urography. Precisely locating the kidneys, however, can be difficult. This article describes a study performed to determine a simple and accurate measurement for kidney location as a guide to obtaining initial nephrotomographic sections. The authors measured the distance from the midplane of the kidney to the posterior skin line on abdominal CT images in 26 patients. This distance averaged one-third the thickness of the abdominal region. The best depth for the nephrotomographic cut was found to be one-third the thickness of the abdomen plus the thickness of any table pad.

Overview of traumatic injury of the thoracic aorta

Traumatic injury of the thoracic aorta is a major clinical concern in patients who sustain deceleration or crush injuries. Several mechanical factors may explain the typical locations of thoracic aortic rupture (aortic isthmus, ascending aorta). Understanding these factors and the pathophysiology involved helps the radiologist to recognize aortic trauma at various imaging examinations. Chest radiography is the initial screening examination, and radiographs are evaluated specifically for signs of mediastinal hematoma, an indication of significant thoracic trauma. The most important of these signs include loss of aortic contour, tracheal deviation, ratio of mediastinal width to chest width, deviation of a nasogastric tube to the right of the T-4 spinous process, and depression of the left main-stem bronchus (> 40 degrees below the horizontal). Computed tomography (CT) is used increasingly when results of chest radiography are equivocal. CT can clearly demonstrate mediastinal hematoma, but this finding is also mimicked by several entities, including atelectatic lung, thymus, and pericardial recesses. Aortography is the standard for diagnosis. Traumatic aortic injury is treated urgently with surgical repair. The rare patient who survives aortic injury without surgery may develop a chronic pseudoaneurysm.

Treatment of HeLa cells with bacterial water extracts inhibits Shigella flexneri invasion

Pathogenesis mediated by Shigella flexneri requires invasion of the gastrointestinal epithelium. It has been previously shown that HeLa cells challenged with S. flexneri show alterations in their phosphotyrosine-containing protein profile. In this report, we demonstrated that bacterial water extracts (WE) abrogated the invasion of HeLa cells by S. flexneri in a dose-dependent manner. A proteinaceous component of S. flexneri was shown to be responsible for this inhibitory activity. Proteins encoded on the 140-MDa plasmid were not responsible for the observed inhibition. WE from other Gram-negative bacteria also inhibited Shigella invasion of HeLa cells pretreated with WE showed changes in the profile and the intensity of phosphotyrosine-containing protein bands. These data were consistent with a surface protein component in WE which initiated aberrant host cell signaling at the membrane which may account for the inhibition of bacterial entry.

The perirenal space: relationship of pathologic processes to normal retroperitoneal anatomy

The perirenal space may be involved by disease processes that arise within or outside the perirenal space. Key anatomic details that dictate the features of perirenal processes include the renal capsule, the perirenal septa, the renal fascia, and the conic shape and inferomedial orientation of the perirenal space. Superiorly, the perirenal space is open to the bare area of the liver. The perirenal spaces communicate with one another at the level of the lower lumbar vertebrae. The hallmark of perirenal infection is localized or diffuse gas. Chronic urinoma appears as an encapsulated cystic mass, often aligned parallel with the perirenal space. Fat within an apparent spontaneous hematoma of the perirenal space suggests angiomyolipoma. Renal cell carcinoma, lymphoma, and melanoma are the most common causes of discrete solid masses in the perirenal space; metastases occur due to the characteristic lymphatic and vascular supply of the space. Amyloidosis and fibrosis create a nonspecific rind of soft tissue around the kidneys. Diaphragmatic pseudotumor produces a linear "lesion" in the perirenal space.

Trans effects in nitric oxide binding to myoglobin cavity mutant H93G

When nitric oxide (NO) binds to heme proteins, it exerts a repulsive trans effect on the proximal ligand, resulting in weakening or rupture of the proximal ligand-iron bond. The general question of whether NO binding generates a five-coordinate complex with proximal ligand release is important for the function of enzymes such as guanylate cyclase. This question can be addressed by studying NO binding to the myoglobin cavity mutant H93G, where the proximal histidine has been replaced by glycine. When this protein is expressed in the presence of imidazole (Im), an imidazole molecule occupies the proximal cavity and serves as a ligand to the iron [Barrick, D. (1994) Biochemistry 33, 6546-6554]. This proximal imidazole can be exchanged for a variety of exogenous ligands [DePillis, G.D., Decatur, S. M., Barrick, D., & Boxer, S.G. (1994) J. Am. Chem. Soc. 116, 6981-6982]. While CO binds to H93G(Im) to form a stable six-coordinate complex similar to that of the wild type and NO binds to wild-type myoglobin to form a six-coordinate complex, we find that the binding of NO to H93G(Im) under similar conditions results in the cleavage of the exogenous imidazole-iron bond at neutral pH, leaving a five-coordinate heme-NO complex, H93G-NO, inside the protein. When a large excess of imidazole is added to this five-coordinate NO complex, a six-coordinate complex can be formed; thus, the binding constant of a sixth ligand to the five-coordinate H93G-NO complex can be measured. This is found to be several orders of magnitude smaller than the binding constant of Im to the carbonmonoxy, deoxy, or the metcyano forms of protein. By replacement of Im with methyl-substituted imidazoles which have hindered or strained binding conformations, this binding constant can be reduced further and some of the factors responsible for favoring the five-coordinate form can be elucidated. Thus, the cavity mutant H93G provides a novel model system for studying the factors that control the coordination state of NO complexes of heme proteins and serves as a bridge between synthetic heme model complexes in simple solvents and site-directed mutants in the structured environment found in proteins.

Fast events in protein folding: helix melting and formation in a small peptide

The helix is a common secondary structural motif found in proteins, and the mechanism of helix-coil interconversion is key to understanding the protein-folding problem. We report the observation of the fast kinetics (nanosecond to millisecond) of helix melting in a small 21-residue alanine-based peptide. The unfolding reaction is initiated using a laser-induced temperature jump and probed using time-resolved infrared spectroscopy. The model peptide exhibits fast unfolding kinetics with a time constant of 160 +/- 60 ns at 28 degrees C in response to a laser-induced temperature jump of 18 degrees C which is completed within 20 ns. Using the unfolding time and the measured helix-coil equilibrium constant of the model peptide, a folding rate constant of approximately 6 x 10(7) s-1 (t1/2 = 16 ns) can be inferred for the helix formation reaction at 28 degrees C. These results demonstrate that secondary structure formation is fast enough to be a key event at early times in the protein-folding process and that helices are capable of forming before long range tertiary contacts are made.

Beta adrenergic blockade does not improve effort tolerance in patients with mitral stenosis in sinus rhythm

OBJECTIVES

This study was designed to assess the effects of beta-blockade on cardiopulmonary exercise performance in symptomatic patients with tight mitral stenosis in sinus rhythm.

BACKGROUND

The role of beta-blockers in these patients has been controversial and assessment of effort tolerance using treadmill exercise time has produced conflicting results.

METHODS

Nineteen patients with isolated symptomatic (New York Heart Association class II or III) mitral stenosis received a beta-blocker (acebutalol or atenolol) or matching placebo for one week each in a randomized double-blind crossover fashion. Exercise on a treadmill with real time gas exchange analysis was performed six times over 4 weeks in each patient. The test was further repeated once within a week of percutaneous mitral valvotomy.

RESULTS

Heart rate at rest and during peak exercise was significantly lower with beta-blockade compared to control state or placebo treatment. Mean peak oxygen consumption did not differ significantly between treatment groups. When patients were arbitrarily classified into those with (group I, heart rate < or = 130.min-1) and those without (group II, heart rate > or = 131.min-1) adequate beta-blockade, there was a significant difference in peak VO2. The peak VO2 for group I: 14.0 +/- 3.2 vs 17.5 +/- 4.0 ml.min-1.kg-1; peak VO2 for group II: 17.2 +/- 2.4 vs 18.0 +/- 2.4 ml.min-1.kg-1 (beta-blockade vs control state respectively). Treadmill exercise time did not differ between treatment groups. The slope of minute ventilation (MV) and carbon dioxide (CO2) excretion, and instantaneous carbon dioxide ventilatory equivalent (MV/VCO2) was unchanged with beta-blocker therapy indicating no improvement in ventilatory performance.

CONCLUSIONS

Beta-blocker therapy in tight mitral stenosis appears to have no beneficial effect on aerobic capacity, nor does it improve ventilatory performance. Adequate beta-blockade may adversely effect peak oxygen consumption.

The CT nephrogram: implications for evaluation of urinary tract disease

The urographic nephrogram is an important indicator of underlying functional and structural renal disease. With expansions in use of cross-sectional imaging, the computed tomographic (CT) nephrogram (ie, contrast material enhancement within the renal parenchyma) has assumed a greater role in the evaluation of urinary tract disorders. Both quantitative and qualitative nephrographic abnormalities are well demonstrated by CT, including global or segmental absence or persistence of the nephrogram, slowed temporal progression, striated pattern, and rim pattern. Global absence is nearly always unilateral and is most often seen with blunt abdominal trauma with renal pedicle injury. Segmental absence is attributable to focal renal infarction, most likely due to arterial emboli. Global persistence, which is much more common than segmental persistence, may be unilateral (caused by renal artery stenosis, renal vein thrombosis, or urinary tract obstruction) or bilateral (due to systemic hypotension, intratubular obstruction, or abnormalities in tubular function). Striated nephrograms may be unilateral or bilateral and are caused by ureteric obstruction, acute pyelonephritis, contusion, renal vein thrombosis, tubular obstruction, hypotension, and autosomal recessive polycystic kidney disease. The rim pattern is most often associated with renal infarction and occasionally with acute tubular necrosis and renal vein thrombosis. Careful evaluation of the CT nephrogram is an integral part of the abdominal CT examination.

Immunodepletion EMSA: a novel method to identify proteins in a protein-DNA complex

Images

Interureteric ridge edema: incidence and etiology

BACKGROUND

Interureteric ridge edema may be seen at intravenous urography (IVU) and is related to acute lower ureteral obstruction, trauma, or calculi. The purpose of this study was to explore the relationship between interureteric ridge edema and acute distal ureteral obstruction caused by ureteral calculi.

METHODS

A total of 338 patients who had IVU for various indications during a 6-month period were reviewed for the presence of interureteric ridge edema.

RESULTS

Interureteric ridge edema was seen in 12 (4%) of 338 patients, all with acute lower ureteral obstruction from stones. Interureteric ridge edema was best demonstrated with the partially filled bladder film or post-void bladder film in all cases.

CONCLUSION

Interureteric ridge edema is most commonly caused by stone-induced distal ureteral obstruction and is less commonly seen with recent passage of a stone or other etiologies. Interureteric ridge edema was present in 26% of patients with acute lower ureteral obstruction.

Staging of renal adenocarcinoma: role of various imaging procedures

Since the only successful curative treatment of renal adenocarcinoma is surgery, accurate radiologic information is crucial during initial tumor staging for optimal operative planning. Accurate radiologic staging can be achieved by use of proper imaging techniques, usually a combination of contrast-enhanced CT or multiplanar MR imaging with fast scanning techniques. These techniques permit the demonstration of regional lymph nodes, vascular extension, and distant metastases. Sonography and inferior venacavography are used occasionally to supplement the information obtained from CT or MR imaging. We review the principles of staging of renal adenocarcinoma, emphasizing the strengths and weaknesses of each imaging technique.

Shigella flexneri-HeLa cell interactions: a putative role for host cell protein kinases

Epithelial cell invasion has been shown to be a prerequisite for Shigella flexneri virulence. Recently, we have documented the induction of transcription factor DNA binding activities as a result of S. flexneri challenge of HeLa cells. In this report, we show that HeLa cells challenged with S. flexneri display differences in phosphotyrosine-containing proteins. These changes are detected as early as 5 min post-challenge. Challenge with a noninvasive ipaB mutant strain resulted in the induction of a similar, but less intense, profile of phosphotyrosine-containing host cell proteins. Phosphotyrosine-containing proteins could be detected in S. flexneri, but were unique from those detected following HeLa cell challenge. S. flexneri invasion of HeLa cell monolayers was reduced by treatment with protein kinase inhibitors. These data suggest a role for protein kinases in the initial response of host cells to S. flexneri.

Cost-effective filming sequence for intravenous urography

To define an intravenous urography (IVU) film sequence that maximizes sensitivity and minimizes filming costs, we evaluated the effect of omitting films from a standard IVU sequence. We reviewed 82 IVU series that demonstrated abnormalities. Each series comprised 11 films: preliminary abdominal radiograph and nephrotomogram, three 1-minute nephrotomograms, 5-minute abdominal film, 10-minute radiograph with abdominal compression, one frontal and two oblique 15-minute films, and postvoid film. Sensitivity was determined for each film. Eighty-two standard IVUs showed 120 abnormalities. Omitting any one film from the sequence decreased sensitivity by 0% to 12%. Omitting the preliminary film resulted in failure to detect 15 abnormalities (12%). Omitting any nephrotomogram, the 10-minute compression view, or either 15-minute oblique film did not decrease sensitivity. Omitting combinations of these films lowered overall sensitivity. The postvoid film was essential in only one case. We conclude that a sequence of nine radiographs decreases film and processing expenses by 18% without sacrificing sensitivity. Sequences with fewer films substantially reduce detection of common urinary tract abnormalities.

Gender-related differences in expression of murine glutathione S-transferases and their induction by butylated hydroxyanisole

The basal levels of mu and pi class glutathione S-transferases RNA were 18-fold higher in the male mouse liver as compared with the female. When 0.75% (w/w) BHA was included in the diet it altered the RNA levels of alpha, mu, pi GST classes and mGSTA4-4 in a tissue and sex specific manner. The most marked induction of RNA was seen for the mu class GSTs of female liver, lung and kidney (52, 10 and 8-fold, respectively), and of male liver and kidney (25 and 3.5-fold, respectively), the pi class GSTs of female liver, lung, and kidney (11, 10, and 5-fold, respectively), and mGSTA4-4 of female liver (4-fold). The effect of BHA on the induction of the mu and pi class GST RNA was 2-9 fold greater in female as compared with male tissues. The degree of induction of GST RNA did not correlate directly with changes in GST protein indicating that post-transcriptional events regulating GST expression may be affected by BHA particularly for GST mu and mGSTA4-4.

Spectroscopic characterization of cytochrome ba3, a terminal oxidase from Thermus thermophilus: comparison of the a3/CuB site to that of bovine cytochrome aa3

Unliganded and cyano derivatives of cytochrome ba3 from Thermus thermophilus have been examined by UV-vis, EPR, and resonance Raman spectroscopies. Species of cytochrome ba3 investigated include its resting, as-isolated, fully oxidized state, the fully reduced, unliganded enzyme, the one-electron-reduced cyano complex, the three-electron-reduced cyano complex, and the fully reduced cyano complex. Results are compared to those obtained from similar adducts of bovine cytochrome aa3, in particular, the fully reduced cyano complex. Our objective was to identify structural similarities and differences at the ligand-binding binuclear site of the two enzymes. We observed that the inner core skeletal vibrations of cytochrome a3 are the same for similar adducts of the bacterial ba3 and mammalian aa3, indicating similar spin and iron-porphyrin coordination properties resulting in comparable porphyrin core geometries. On the other hand, many of the vibrational frequencies associated with the formyl and vinyl peripheral substituents, and the outer pyrrole carbon atoms differ between the bovine and bacterial enzymes. Use of 57Fe labeled ba3 allows identification of two separate vFe-N(His) frequencies displayed by the fully reduced, unliganded cytochrome. These frequencies, occurring at 193 and 209 cm-1, are ascribed to distinct protein conformers, which are best evidenced by the Fe-N(His) vibrations. This result is again in contrast to the bovine enzyme which has been shown by others to display a single Fe-N(His) stretching frequency at 214 cm-1. The low-frequency Fea3(2+)-CN- vibrations of the three-electron and fully reduced cyano complexes of cytochrome ba3 are identified by using 15N and 13C isotopomers of CN-. These spectral signatures are identical to those reported earlier for the one-electron-reduced cyanide adduct (cytochrome a3 reduced), showing that the Fea3(2+)-CN- vibrational frequencies are independent of the redox states of the other three metal centers. Similarly, the CuB2+ EPR signatures appear similar in both the one-electron- and three-electron-reduced cyanide adducts. On the other hand, the electronic absorption spectra of ferrous alpha 3-CN- show systematic red-shifts of the alpha band as each of the other metal centers is reduced, and other, more subtle, differences in the electronic absorptions of the three-electron-reduced and four-electron-reduced cyanide adducts are revealed in the difference spectra. The relevance of these findings toward explaining the different cyanide binding and redox chemistry described herein and toward establishing the extent of structural analogy between the oxygen binding sites of the two proteins is discussed.

Picosecond infrared study of the photodynamics of carbonmonoxy-cytochrome c oxidase

Time-resolved infrared (TRIR) techniques have been employed to study the reactions of carbon monoxide with the cytochrome alpha 3-Cu(B) site of cytochrome c oxidase (CcO). The ligation dynamics immediately following photodissociation have been investigated using picosecond TRIR spectroscopy and linear dichroism. The rate of photoinitiated transfer of CO from cytochrome alpha 3 to CuB was measured directly by monitoring the development of the transient CuBCO absorption. In less than 1 ps, a stationary CuBCO spectrum develops, which together with the CO infrared linear dichroism is constant until the CO dissociates from CuB on a microsecond time scale. These observations indicate that the CO is transferred between metals and reaches its equilibrium conformation in less than 1 ps. This unprecedented ligand transfer rate has profound implications with regard to the structure and dynamics of the cytochrome alpha 3-CuB site, the functional architecture of the protein, and coordination dynamics in general.