Corrigendum: Iatrogenic air embolism: pathoanatomy, thromboinflammation, endotheliopathy, and therapies

[This corrects the article DOI: 10.3389/fimmu.2023.1230049.].

Iatrogenic air embolism: pathoanatomy, thromboinflammation, endotheliopathy, and therapies

Iatrogenic vascular air embolism is a relatively infrequent event but is associated with significant morbidity and mortality. These emboli can arise in many clinical settings such as neurosurgery, cardiac surgery, and liver transplantation, but more recently, endoscopy, hemodialysis, thoracentesis, tissue biopsy, angiography, and central and peripheral venous access and removal have overtaken surgery and trauma as significant causes of vascular air embolism. The true incidence may be greater since many of these air emboli are asymptomatic and frequently go undiagnosed or unreported. Due to the rarity of vascular air embolism and because of the many manifestations, diagnoses can be difficult and require immediate therapeutic intervention. An iatrogenic air embolism can result in both venous and arterial emboli whose anatomic locations dictate the clinical course. Most clinically significant iatrogenic air emboli are caused by arterial obstruction of small vessels because the pulmonary gas exchange filters the more frequent, smaller volume bubbles that gain access to the venous circulation. However, there is a subset of patients with venous air emboli caused by larger volumes of air who present with more protean manifestations. There have been significant gains in the understanding of the interactions of fluid dynamics, hemostasis, and inflammation caused by air emboli due to in vitro and in vivo studies on flow dynamics of bubbles in small vessels. Intensive research regarding the thromboinflammatory changes at the level of the endothelium has been described recently. The obstruction of vessels by air emboli causes immediate pathoanatomic and immunologic and thromboinflammatory responses at the level of the endothelium. In this review, we describe those immunologic and thromboinflammatory responses at the level of the endothelium as well as evaluate traditional and novel forms of therapy for this rare and often unrecognized clinical condition.

Receptor activator of nuclear factor-kappa B is enriched in CD9-positive extracellular vesicles released by osteoclasts

Aim

Receptor activator of nuclear factor-kappa B (RANK)-containing extracellular vesicles (EVs) bind RANK-Ligand (RANKL) on osteoblasts, and thereby simultaneously inhibit bone resorption and promote bone formation. Because of this, they are attractive candidates for therapeutic bone anabolic agents. Previously, RANK was detected in 1 in every 36 EVs from osteoclasts by immunogold electron microscopy. Here, we have sought to characterize the subpopulation of EVs from osteoclasts that contains RANK in more detail.

Methods

The tetraspanins CD9 and CD81 were localized in osteoclasts by immunofluorescence. EVs were visualized by transmission electron microscopy. A Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS) and immunoaffinity isolations examined whether RANK is enriched in specific types of EVs.

Results

Immunofluorescence showed CD9 was mostly on or near the plasma membrane of osteoclasts. In contrast, CD81 was localized deeper in the osteoclast's cytosolic vesicular network. By interferometry, both CD9 and CD81 positive EVs from osteoclasts were small (56-83 nm in diameter), consistent with electron microscopy. The CD9 and CD81 EV populations were mostly distinct, and only 22% of the EVs contained both markers. RANK was detected by SP-IRIS in 2%-4% of the CD9-containing EVs, but not in CD81-positive EVs, from mature osteoclasts. Immunomagnetic isolation of CD9-containing EVs from conditioned media of osteoclasts removed most of the RANK. A trace amount of RANK was isolated with CD81.

Conclusion

RANK was enriched in a subset of the CD9-positive EVs. The current study provides the first report of selective localization of RANK in subsets of EVs.

Type B Lactic Acidosis in a Patient with Mantle Cell Lymphoma

Type B lactic acidosis is an uncommon medical emergency in which acid production overwhelms hepatic clearance. This specific etiology of lactic acidosis occurs without organ hypoperfusion and has been most commonly described in patients with hematologic malignancies but also in patients with solid tumors. The mechanism by which cancer cells switch their glucose metabolism toward increasingly anaerobic glycolytic phenotypes has been described as the "Warburg effect." Without treating the underlying malignancy, the prognosis for patients diagnosed with malignancy-related type B lactic acidosis is extremely poor. Here, we present a case of a 66-year-old male who was diagnosed with type B lactic acidosis secondary to mantle cell lymphoma. Bicarbonate drip was started to correct the lactic acidosis. The patient was also immediately treated with rituximab chemotherapy combined with rasburicase to avoid the hyperuricemia associated with tumor lysis syndrome. He responded to the early treatment and was discharged with normal renal function. Type B lactic acidosis secondary to hematologic malignancy is important to recognize. In order to successfully treat this syndrome, early diagnosis and simultaneous treatment of the imbalance of lactic acid levels and the underlying malignancy are necessary.

Reply to Bareille et al. Are Viscoelastometric Assays of Old Generation Ready for Disposal? Comment on "Volod et al. Viscoelastic Hemostatic Assays: A Primer on Legacy and New Generation Devices. J. Clin. Med. 2022, 11, 860"

We are pleased to see that Bareille et al. have written a Commentary: "Are viscoelastometric assays of old generation ready for disposal?" [...].

SHock-INduced Endotheliopathy (SHINE): A mechanistic justification for viscoelastography-guided resuscitation of traumatic and non-traumatic shock

Irrespective of the reason for hypoperfusion, hypocoagulable and/or hyperfibrinolytic hemostatic aberrancies afflict up to one-quarter of critically ill patients in shock. Intensivists and traumatologists have embraced the concept of SHock-INduced Endotheliopathy (SHINE) as a foundational derangement in progressive shock wherein sympatho-adrenal activation may cause systemic endothelial injury. The pro-thrombotic endothelium lends to micro-thrombosis, enacting a cycle of worsening perfusion and increasing catecholamines, endothelial injury, de-endothelialization, and multiple organ failure. The hypocoagulable/hyperfibrinolytic hemostatic phenotype is thought to be driven by endothelial release of anti-thrombogenic mediators to the bloodstream and perivascular sympathetic nerve release of tissue plasminogen activator directly into the microvasculature. In the shock state, this hemostatic phenotype may be a counterbalancing, yet maladaptive, attempt to restore blood flow against a systemically pro-thrombotic endothelium and increased blood viscosity. We therefore review endothelial physiology with emphasis on glycocalyx function, unique biomarkers, and coagulofibrinolytic mediators, setting the stage for understanding the pathophysiology and hemostatic phenotypes of SHINE in various etiologies of shock. We propose that the hyperfibrinolytic phenotype is exemplified in progressive shock whether related to trauma-induced coagulopathy, sepsis-induced coagulopathy, or post-cardiac arrest syndrome-associated coagulopathy. Regardless of the initial insult, SHINE appears to be a catecholamine-driven entity which early in the disease course may manifest as hyper- or hypocoagulopathic and hyper- or hypofibrinolytic hemostatic imbalance. Moreover, these hemostatic derangements may rapidly evolve along the thrombohemorrhagic spectrum depending on the etiology, timing, and methods of resuscitation. Given the intricate hemochemical makeup and changes during these shock states, macroscopic whole blood tests of coagulative kinetics and clot strength serve as clinically useful and simple means for hemostasis phenotyping. We suggest that viscoelastic hemostatic assays such as thromboelastography (TEG) and rotational thromboelastometry (ROTEM) are currently the most applicable clinical tools for assaying global hemostatic function-including fibrinolysis-to enable dynamic resuscitation with blood products and hemostatic adjuncts for those patients with thrombotic and/or hemorrhagic complications in shock states.

COVID-associated non-vasculitic thrombotic retiform purpura of the face and extremities: A case report

SARS-CoV-2 infection can manifest many rashes. However, thrombotic retiform purpura rarely occurs during COVID-19 illness. Aggressive anti-COVID-19 therapy with a high-dose steroid regimen led to rapid recovery. This immunothrombotic phenomenon likely represents a poor type 1 interferon response and complement activation on the endothelial surface in response to acute infection.

Visuomotor control in mice and primates

We conduct a comparative evaluation of the visual systems from the retina to the muscles of the mouse and the macaque monkey noting the differences and similarities between these two species. The topics covered include (1) visual-field overlap, (2) visual spatial resolution, (3) V1 cortical point-image [i.e., V1 tissue dedicated to analyzing a unit receptive field], (4) object versus motion encoding, (5) oculomotor range, (6) eye, head, and body movement coordination, and (7) neocortical and cerebellar function. We also discuss blindsight in rodents and primates which provides insights on how the neocortex mediates conscious vision in these species. This review is timely because the field of visuomotor neurophysiology is expanding beyond the macaque monkey to include the mouse; there is therefore a need for a comparative analysis between these two species on how the brain generates visuomotor responses.

RANKL and RANK in extracellular vesicles: surprising new players in bone remodeling

Receptor activator of nuclear factor kappa B-ligand (RANKL), its receptor RANK, and osteoprotegerin which binds RANKL and acts as a soluble decoy receptor, are essential controllers of bone remodeling. They also play important roles in establishing immune tolerance and in the development of the lymphatic system and mammary glands. In bone, RANKL stimulates osteoclast formation by binding RANK on osteoclast precursors and osteoclasts. This is required for bone resorption. Recently, RANKL and RANK have been shown to be functional components of extracellular vesicles (EVs). Data linking RANKL and RANK in EVs to biological regulatory roles are reviewed, and crucial unanswered questions are examined. RANKL and RANK are transmembrane proteins and their presence in EVs allows them to act at a distance from their cell of origin. Because RANKL-bearing osteocytes and osteoblasts are often spatially distant from RANK-containing osteoclasts in vivo, this may be crucial for the stimulation of osteoclast formation and bone resorption. RANK in EVs from osteoclasts has the capacity to stimulate a RANKL reverse signaling pathway in osteoblasts that promotes bone formation. This serves to couple bone resorption with bone formation and has inspired novel bifunctional therapeutic agents. RANKL- and RANK- containing EVs in serum may serve as biomarkers for bone and immune pathologies. In summary, EVs containing RANKL and RANK have been identified as intercellular regulators in bone biology. They add complexity to the central signaling network responsible for maintaining bone. RANKL- and RANK-containing EVs are attractive as drug targets and as biomarkers.

Technique to manage intraoperative cuff leak from damaged endotracheal tube pilot balloon

We report a technique that was utilized to manage an intraoperative airway complication occurring during orthognathic surgery wherein the endotracheal tube pilot balloon was inadvertently damaged during the procedure. Readily available operating room materials were used to safely and rapidly repair the damaged endotracheal tube pilot balloon. This allowed the perioperative team to avoid emergent endotracheal tube exchange and potential airway complications.

Metagenomic of clinically diseased and healthy broiler affected with respiratory disease complex

In recent past, the respiratory infection has emerged as a great challenge to the poultry farmers. Various pathogens including Avian pneumovirus (APV), Avian influenza virus (AIV), Infectious bronchitis virus (IBV) and Newcastle disease virus (NDV), Avibacterium paragallinarum, Ornithobacterium rhinotracheale (ORT), Mycoplasma synoviae (MS), Mycoplasma gallisepticum (MG) and Avian pathogenic Escherichia coli (APEC) are involved in the respiratory disease complex in birds [1], [2] (Bradbury, 1984; Roussan et al., 2008). Hence, respiratory disease complex is the most serious disease affecting to poultry and causes heavy economic losses in the poultry industry worldwide [3] (Murthy et al., 2008). In recent years, metagenomics is powerful analyzing tool for detection of pathogens directly from clinical samples without any prior knowledge of the organism in a given sample [4], [5] (Schuster, 2008; Pereira et al., 2010). High throughput Next-Generation-Sequencing technology was used for sequencing the isolated genomic DNA. These data provides an insight about taxonomic and functional status of microorganisms responsible for causing respiratory infection in broiler. The data of these metagenome are available in the BioSample Submission Portal as Bioproject PRJNA339659 and SRA accession number SRR5997823, SRR5992854, SRR6037376, SRR6024702, SRR6012248 and SRR6008913.

Improving bone marrow biopsy quality through peer discussion and data comparisons: A single institution experience

INTRODUCTION

Bone marrow biopsy (BMB) is crucial for the diagnosis, staging, and monitoring of a variety of hematologic diseases. Obtaining an adequate BMB can be challenging given the need to balance patient comfort with acquisition of high quality specimens. We had observed variable BMB quality at our institution with poor quality specimens sometimes affecting diagnosis. We thus undertook this quality improvement (QI) project to improve the quality of diagnostic BMB specimens.

METHODS

We used an A3 QI process to identify factors possibly influencing BMB quality. We collected baseline data on 211 BMB, with short and long-term follow-up data on a further 382 cases. We used clinical conferences to discuss data, perform peer comparisons and identify strategies to create a sustainable improvement in BMB quality.

RESULTS

Baseline data showed that BMB length was influenced most by the individual performer, with some influence of needle gauge. Other factors such as sedation, BMB indication were noncontributory. BMB lengths improved following performer education and individual performer data comparisons (15.2 mm post vs 12.8 mm baseline, P < .0001) and with use of an 8- rather than 11-gauge needle (18.3 mm 8-gauge vs 13.3 mm 11-gauge P < .0001), and were sustained over the long term.

CONCLUSIONS

Education on BMB standards, sharing of performer data, and changing needle gauge are relatively straightforward methods to improve BMB quality, leading to easier pathology diagnosis.

Cerebrovascular Complications of Diabetes: Alpha Glucosidase Inhibitor as Potential Therapy

Increased risk of cerebrovascular accident in diabetes cannot be fully explained by traditional risk factors. Epidemiological studies show that postprandial hyperglycemia is strongly associated with cerebrovascular events and cerebrovascular-associated mortality. Postprandial hyperglycemia contributes to vascular damage by several mechanisms such as endothelial dysfunction, arthrosclerosis, oxidative stress, inflammation, and hypercoagulability. Hyperglycemia has deleterious effects on the vascular endothelium and leads to the development of cerebrovascular disease. Thus, an important strategy to reduce cerebrovascular risk in patients with diabetes is to reduce postprandial hyperglycemia. Glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, and α-glucosidase inhibitors predominantly reduce postprandial plasma glucose levels. Among all of these, α-glucosidase inhibitors reduces postprandial hyperglycemia by delaying carbohydrate absorption from the intestine and this mechanism provides glycemic control without exacerbating coexisting cerebrovascular risk factors. Good glycemic control is proven to reduce the risk of cardiovascular complications, but equivalent evidence for cerebrovascular risk reduction is lacking. This review examines the evidences that postprandial hyperglycemia plays a major role in vascular damage, along with the complex interplay between hyperglycemia and coexisting risk factors. Furthermore, the mechanism by which α-glucosidase inhibitors may prevent this vascular damage as well as risk of hypoglycemia with α-glucosidase inhibitors are examined. Thus, this review suggests that α-glucosidase inhibitors are useful in reducing the risk of cerebrovascular events in patients with diabetes.

Five-Year Trend in the Number of Dermatologic Clinical Drug Trials Registered on ClinicalTrials.gov

BACKGROUND

There is a reported global decrease in the number of clinical trials conducted in recent years. We aimed to determine if this declining trend can be extrapolated to dermatologic clinical trials.

METHODS

We conducted a query of ClinicalTrials.gov for dermatologic clinical trials from 2009 to 2013 for 6 common skin conditions: acne, psoriasis, rosacea, eczema and atopic dermatitis, actinic keratosis, and skin cancer. Results were sorted by condition and number of study subjects. This study did not involve any participants apart from the researchers.

RESULTS

Although there is an increasing trend in the number of trials performed annually, the results were not significant (P =.08). The average number of patients per study has not significantly changed (P =.12), but there was a significant increase in the number of large studies (201+ subjects) conducted over time (P =.002). Although there was significant variation based on dermatologic condition studied (global statistic P=.01), only skin cancer demonstrated a significant change in the number of studies registered annually (β=10.6 studies/year, P =.04).

CONCLUSIONS AND RELEVANCE

The sky does not appear to be falling, at least not yet, with regard to continued development of treatments for patients with skin disease.

Production of biocontrol traits by banana field fluorescent Pseudomonads and comparison with chemical fungicide

Pseudomonas aeruginosa isolated from banana field rhizosphere produced different antifungal metabolites like bactriocin, hydrogen cyanide and siderophore. Bacteriocinogenic, siderophoregenic, and HCN rich broth of isolate inhibited the growth of phytopathogen like Aspergilus niger, Aspergilus flavus, Fusarium oxysporum and Alternaria alternata. The isolate exhibited more antifungal activity and comparatively low MIC vis-a-vis commonly used copper based systemic chemical fungicide;bil cop.

Effect of ventilation on cerebral oxygenation in patients undergoing surgery in the beach chair position: a randomized controlled trial

BACKGROUND

Surgery in the beach chair position (BCP) may reduce cerebral blood flow and oxygenation, resulting in neurological injuries. The authors tested the hypothesis that a ventilation strategy designed to achieve end-tidal carbon dioxide (E'(CO₂)) values of 40-42 mm Hg would increase cerebral oxygenation (Sct(O₂)) during BCP shoulder surgery compared with a ventilation strategy designed to achieve E'(CO₂) values of 30-32 mm Hg.

METHODS

Seventy patients undergoing shoulder surgery in the BCP with general anaesthesia were enrolled in this randomized controlled trial. Mechanical ventilation was adjusted to maintain an E'(CO₂) of 30-32 mm Hg in the control group and an E'(CO₂) of 40-42 mm Hg in the study group. Cerebral oxygenation was monitored continuously in the operating theatre using near-infrared spectroscopy. Baseline haemodynamics and Sct(O₂) were obtained before induction of anaesthesia, and these values were then measured and recorded continuously from induction of anaesthesia until tracheal extubation. The number of cerebral desaturation events (CDEs) (defined as a ≥20% reduction in Sct(O₂) from baseline values) was recorded.

RESULTS

No significant differences between the groups were observed in haemodynamic variables or phenylephrine interventions during the surgical procedure. Sct(O₂) values were significantly higher in the study 40-42 group throughout the intraoperative period (P<0.01). In addition, the incidence of CDEs was lower in the study 40-42 group (8.8%) compared with the control 30-32 group (55.6%, P<0.0001).

CONCLUSIONS

Cerebral oxygenation is significantly improved during BCP surgery when ventilation is adjusted to maintain E'(CO₂) at 40-42 mm Hg compared with 30-32 mm Hg.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT01546636.

Separation of intra-S checkpoint protein contributions to DNA replication fork protection and genomic stability in normal human fibroblasts

The ATR-dependent intra-S checkpoint protects DNA replication forks undergoing replication stress. The checkpoint is enforced by ATR-dependent phosphorylation of CHK1, which are mediated by the TIMELESS-TIPIN complex and CLASPIN. Although loss of checkpoint proteins is associated with spontaneous chromosomal instability, few studies have examined the contribution of these proteins to unchallenged DNA metabolism in human cells that have not undergone carcinogenesis or crisis. Furthermore, the TIMELESS-TIPIN complex and CLASPIN may promote replication fork protection independently of CHK1 activation. Normal human fibroblasts (NHF) were depleted of ATR, CHK1, TIMELESS, TIPIN or CLASPIN and chromosomal aberrations, DNA synthesis, activation of the DNA damage response (DDR) and clonogenic survival were evaluated. This work demonstrates in NHF lines from two individuals that ATR and CHK1 promote chromosomal stability by different mechanisms that depletion of CHK1 produces phenotypes that resemble more closely the depletion of TIPIN or CLASPIN than the depletion of ATR, and that TIMELESS has a distinct contribution to suppression of chromosomal instability that is independent of its heterodimeric partner, TIPIN. Therefore, ATR, CHK1, TIMELESS-TIPIN and CLASPIN have functions for preservation of intrinsic chromosomal stability that is separate from their cooperation for activation of the intra-S checkpoint response to experimentally induced replication stress. These data reveal a complex and coordinated program of genome maintenance enforced by proteins known for their intra-S checkpoint function.

Timeless functions independently of the Tim-Tipin complex to promote sister chromatid cohesion in normal human fibroblasts

The Timeless-Tipin complex and Claspin are mediators of the ATR-dependent activation of Chk1 in the intra-S checkpoint response to stalled DNA replication forks. Tim-Tipin and Claspin also contribute to sister chromatid cohesion (SCC) in various organisms, likely through a replication-coupled process. Some models of the establishment of SCC posit that interactions between cohesin rings and replisomes could result in physiological replication stress requiring fork stabilization. The contributions of Timeless, Tipin, Claspin, Chk1 and ATR to SCC were investigated in genetically stable, human diploid fibroblast cell lines. Whereas Timeless, Tipin and Claspin showed similar contributions to UVC-induced activation of Chk1, siRNA-mediated knockdown of Timeless induced a 100-fold increase in sister chromatid discohesion, whereas the inductive effects of knocking down Tipin, Claspin and ATR were 4-20-fold. Knockdown of Chk1 did not significantly affect SCC. Consistent findings were obtained in two independently derived human diploid fibroblast lines and support a conclusion that SCC in human cells is strongly dependent on Timeless but independent of Chk1. Furthermore, the 10-fold difference in discohesion observed when depleting Timeless versus Tipin indicates that Timeless has a function in SCC that is independent of the Tim-Tipin complex, even though the abundance of Timeless is reduced when Tipin is targeted for depletion. A better understanding of how Timeless, Tipin and Claspin promote SCC will elucidate non-checkpoint functions of these proteins at DNA replication forks and inform models of the establishment of SCC.

The human placenta expresses CYP17 and generates androgens de novo

INTRODUCTION

The human placenta is believed to have insignificant CYP17 expression, rendering it dependent on the maternal and fetal compartments for the necessary androgenic precursors to yield the high levels of estrogens seen in pregnancy.

OBJECTIVE

The aim of the study was to analyze whether the human trophoblast is capable of expressing CYP17 and producing androgens de novo.

METHODS

Human trophoblasts from fresh placentas and JEG-3 cells were used for all experiments. CYP17 mRNA analysis was performed via RT-PCR, and protein detection by Western blot and immunohistochemical staining. Steroid products were quantified using RIAs.

RESULTS

CYP17 mRNA was expressed in both cell types. CYP17 protein was detected by Western blotting and localized by immunostaining mainly to the cytoplasm of syncytiotrophoblasts. Measurement of 17α-hydroxyprogesterone, androstenedione, and their aromatized products in the media further demonstrated CYP17 expression and activity in the human trophoblast. Baseline levels of CYP17 steroid products were higher in primary cells and significantly increased in the presence of 22-hydroxycholesterol.

CONCLUSIONS

We have demonstrated CYP17 mRNA and protein expression and activity in human trophoblasts. Considering the precursor concentration, blood flow, and mass of the placenta, we suggest that its contribution of androgens is an important source of estrogen production in pregnancy.

All-optical XOR and XNOR operations at86.4 Gb/s using a pair of semiconductor optical amplifier Mach-Zehnder interferometers

We propose a method for increased-speed all-optical XOR operation using semiconductor optical amplifiers. We demonstrate XOR and XNOR operations at 86.4 Gb/s using a pair of photonic-integrated semiconductor optical amplifier Mach-Zehnder interferometers.

Hyperprolactinaemia

Hyperprolactinaemia is a common condition with varied aetiology. It is more frequent in women, but also seen in men and even in adolescence and childhood. Prolactin is mainly a lactogenic hormone but has other actions. Most cases present with amenorrhoea and infertility and are managed by gynaecologists. However, multidisciplinary involvement may be required in some cases. Evidence relating to aetiology, clinical features, pathogenesis and management has been discussed.

Pharmacodynamics of mivacurium chloride in 13- to 18-yr-old adolescents with thermal injury

BACKGROUND

Burned patients demonstrate resistance to the effects of non-depolarizing blocking drugs as a result of acetylcholine receptor changes. They also have decreased activity of plasma cholinesterase (PCHE), which metabolizes mivacurium. We hypothesized that decreased PCHE activity would decrease metabolism of mivacurium, and counteract the receptor-related resistance following burns.

METHODS

Thirteen burned patients and six controls, aged 13-18 yr were followed in 27 studies. The burned patients were sub-classified as having 10-30% or >30% body surface area burn and were studied whenever possible at < or =6 days, and at 1-12 weeks after the burn. Mivacurium pharmacodynamics were examined following a bolus (0.15 mg kg(-1)) dose, and during and after a continuous infusion.

RESULTS

Following a bolus, the onset time and the maximal effect were similar to controls. Recovery was prolonged in the 10-30% burn group at 1-12 weeks (P<0.008), with a similar trend in the >30% burn group at < or =6 days (P<0.082) compared with controls. The infusion requirements for mivacurium were not increased in the burned groups. The PCHE activity was decreased in all burn groups and was inversely related to recovery following the bolus (r=0.73, P<0.001) and the infusion (r=0.69, P<0.001).

CONCLUSION

In contrast to previous studies with non-depolarizers in burned patients, normal mivacurium doses can produce paralysis, at least as rapidly as in controls, but with a possibility of a prolonged recovery from block. The standard dose of mivacurium in the presence of decreased PCHE activity is in effect, a relative overdose that explains the above findings. Mivacurium is an effective drug for use in burns, irrespective of time after, or magnitude of burn injury.

The association of the glycophorin C exon 3 deletion with ovalocytosis and malaria susceptibility in the Wosera, Papua New Guinea

Erythrocyte polymorphisms, including ovalocytosis, have been associated with protection against malaria. This study in the Wosera, a malaria holoendemic region of Papua New Guinea, examined the genetic basis of ovalocytosis and its influence on susceptibility to malaria infection. Whereas previous studies showed significant associations between Southeast Asian ovalocytosis (caused by a 27- base pair deletion in the anion exchanger 1 protein gene) and protection from cerebral malaria, this mutation was observed in only 1 of 1019 individuals in the Wosera. Polymerase chain reaction strategies were developed to genotype individuals for the glycophorin C exon 3 deletion associated with Melanesian Gerbich negativity (GPCDeltaex3). This polymorphism was commonly observed in the study population (GPCDeltaex3 frequency = 0.465, n = 742). Although GPCDeltaex3 was significantly associated with increased ovalocytosis, it was not associated with differences in either Plasmodium falciparum or P vivax infection measured over the 7-month study period. Future case-control studies will determine if GPCDeltaex3 reduces susceptibility to malaria morbidity.

The primase active site is on the outside of the hexameric bacteriophage T7 gene 4 helicase-primase ring

Gene 4 of bacteriophage T7 encodes a protein (gp4) that can translocate along single-stranded DNA, couple the unwinding of duplex DNA with the hydrolysis of dTTP, and catalyze the synthesis of short RNA oligoribonucleotides for use as primers by T7 DNA polymerase. Electron microscopic studies have shown that gp4 forms hexameric rings, and X-ray crystal structures of the gp4 helicase domain and of the highly homologous RNA polymerase domain of Escherichia coli DnaG have been determined. Earlier biochemical studies have shown that when single-stranded DNA is bound to the hexameric ring, the primase domain remains accessible to free DNA. Given these results, a model was suggested in which the primase active site in the gp4 hexamer is located on the outside of the hexameric ring. We have used electron microscopy and single-particle image analysis to examine T7 gp4, and have determined that the primase active site is located on the outside of the hexameric ring, and therefore provide direct structural support for this model.

Eikenella corrodens infections in children and adolescents: case reports and review of the literature

Eikenella corrodens is a slow-growing, gram-negative, nonmotile, facultative rod that can cause infection in humans. Although the clinical characteristics of Eikenella infections in adults are well described, the literature regarding Eikenella infections in children is lacking. Thirteen cases of Eikenella infection in children and adolescents reported from a hospital and an additional 41 cases from the literature were reviewed. Eikenella species can be serious pediatric pathogens, particularly when there is an exposure to human oral secretions. Empirical therapy used to manage most oropharyngeal flora may be ineffective against Eikenella species. The treatment of choice for children and adolescents who are infected with Eikenella species includes a combination of surgical management and antibiotics.

Vergence dynamics predict fixation disparity

The neural origin of the steady-state vergence eye movement error, called binocular fixation disparity, is not well understood. Further, there has been no study that quantitatively relates the dynamics of the vergence system to its steady-state behavior, a critical test for the understanding of any oculomotor system. We investigate whether fixation disparity can be related to the dynamics of opponent convergence and divergence neural pathways. Using binocular eye movement recordings, we first show that opponent vergence pathways exhibit asymmetric angle-dependent gains. We then present a neural model that combines physiological properties of disparity-tuned cells and vergence premotor cells with the asymmetric gain properties of the opponent pathways. Quantitative comparison of the model predictions with our experimental data suggests that fixation disparity can arise when asymmetric opponent vergence pathways are driven by a distributed disparity code.

The kinetic pathway of RNA binding to the Escherichia coli transcription termination factor Rho

The Escherichia coli transcription termination factor Rho is structurally and functionally homologous to hexameric helicases that assemble into ring structures. Using stopped-flow fluorescence and presteady-state ATPase kinetics, we have determined the kinetic pathway of poly(C) RNA binding to Rho hexamer, both in the presence and in absence of ATP. These studies indicate a four-step sequential mechanism of RNA binding and reveal the respective roles of the primary and secondary RNA binding sites in initiation and ATPase activation of Rho. The primary RNA binding sites of Rho hexamer interact with poly(C) RNA at a diffusion-limited rate constant close to 8 x 10(8) m(-1) s(-1), resulting in the Rho-RNA species PR1, which subsequently isomerizes to PR2 with a rate constant 21 s(-1). The PR2 isomerizes to PR3 with a rate constant of 32 s(-1) in the presence of ATP, and the formation of PR4 from PR3 results in a species that is fully competent in hydrolyzing ATP at the RNA-stimulated rate. The PR3 to PR4 isomerization occurs at a relatively slow rate of 4.1 s(-1); thus, the presteady-state ATPase kinetics show a distinct lag due to the slow initiation step. The interactions of the RNA with the primary sites trigger ring opening, and we propose that during the last two steps, the RNA migrates into the central channel and interacts with the secondary sites, resulting in the activation of the ATPase activity. The primary RNA binding sites, in addition to promoting sequence specific initiation, kinetically facilitate loading of the RNA into the secondary sites, which are relatively inaccessible, since they are present in the central channel. These studies reveal common features used by hexameric helicases to bind nucleic acids in an efficient and specific manner.

Peculiar 2-aminopurine fluorescence monitors the dynamics of open complex formation by bacteriophage T7 RNA polymerase

The kinetics of promoter binding and open complex formation in bacteriophage T7 RNA polymerase was investigated using 2-aminopurine (2-AP) modified promoters. 2-AP serves as an ideal probe to measure the kinetics of open complex formation because its fluorescence is sensitive to both base-unpairing and base-unstacking and to the nature of the neighboring bases. All four 2-AP bases in the TATA box showed an increase in fluorescence with similar kinetics upon binding to the T7 RNA polymerase, indicating that the TATA sequence becomes unpaired in a concerted manner. The 2-AP at -4 showed a peculiarly large increase in fluorescence upon binding to the T7 RNA polymerase. Based on the recent crystal structure of the T7 RNA polymerase-DNA complex, we propose that the large fluorescence increase is due to unstacking of the 2-AP base at -4 from the guanine at -5, during open complex formation. The unstacking may be a critical event in directing and placing the template strand correctly in the T7 RNA polymerase active site upon promoter melting for template directed RNA synthesis. Based on equilibrium fluorescence and stopped-flow kinetic studies, we propose that a fast form of T7 RNA polymerase binds promoter double-stranded DNA by a three-step mechanism. The initial collision complex or a closed complex, ED(c) is formed with a K(d) of 1.8 microm. This complex isomerizes to an open complex, ED(o1), in an energetically unfavorable reaction with an equilibrium constant of 0.12. The ED(o1) further isomerizes to a more stable open complex, ED(o2), with a rate constant around 300 s(-1). Thus, in the absence of the initiating nucleotide, GTP, the overall equilibrium constant for closed to open complex conversion is 0.5 and the net rate of open complex formation is nearly 150 s(-1).

Structure and function of hexameric helicases

Helicases are motor proteins that couple the hydrolysis of nucleoside triphosphate (NTPase) to nucleic acid unwinding. The hexameric helicases have a characteristic ring-shaped structure, and all, except the eukaryotic minichromosomal maintenance (MCM) helicase, are homohexamers. Most of the 12 known hexameric helicases play a role in DNA replication, recombination, and transcription. A human genetic disorder, Bloom's syndrome, is associated with a defect in one member of the class of hexameric helicases. Significant progress has been made in understanding the biochemical properties, structures, and interactions of these helicases with DNA and nucleotides. Cooperativity in nucleotide binding was observed in many, and sequential NTPase catalysis has been observed in two proteins, gp4 of bacteriophage T7 and rho of Escherichia coli. The crystal structures of the oligomeric T7 gp4 helicase and the hexamer of RepA helicase show structural features that substantiate the observed cooperativity, and both are consistent with nucleotide binding at the subunit interface. Models are presented that show how sequential NTP hydrolysis can lead to unidirectional and processive translocation. Possible unwinding mechanisms based on the DNA exclusion model are proposed here, termed the wedge, torsional, and helix-destabilizing models.

Vacuum extraction in modern obstetric practice: a review and critique

The practice of obstetric vacuum extraction is controversial. This article discusses several issues concerning vacuum extraction including maternal and fetal injury risks, failure rates, indications and technique. Recently published articles on these topics are presented and summarized. Throughout this review, vacuum extraction is evaluated against its principal alternatives, forceps and cesarean delivery.

Recognition thresholds for letters with simulated dioptric blur

We examined the effects of simulated dioptric blur on the degradation of visual acuity using digitally filtered letters. Four types of digital filters were applied to 5 letters (C, D, E, O, and S), constructed to the specifications of Sloan optotypes. These filters were: (1) "normal," designed to simulate the positive and negative lobes of the modulation transfer function (MTF) produced by dioptric blur; (2) "truncated," which passed only those spatial frequencies up to the first zero of the MTF; (3) "phase-rectified," which inverted all of the negative lobes of the MTF to positive; and (4) "truncated-plus-negative," which eliminated all positive lobes above the first zero of the MTF. The letter size required to achieve 60%-correct identification was determined for letters that were filtered to simulate +1, +2, and +4 D of blur. Letters subjected to normal, truncated, and truncated-plus-negative filtering had approximately the same acuity threshold, whereas the threshold size for phase-rectified letters was significantly better. Our interpretation of these results is that dioptric blur hinders letter recognition because useful spatial frequency information is limited to that below the first zero of the MTF, and not because of interference from the phase-reversed spatial frequency information above the first zero. Our letter identification thresholds are consistent with recent evidence that the critical information for letter acuity corresponds to approximately 1.5 cycles/letter.

A ring-opening mechanism for DNA binding in the central channel of the T7 helicase-primase protein

We have investigated the mechanism of binding single-stranded DNA (ssDNA) into the central channel of the ring-shaped T7 gp4A' helicase-primase hexamer. Presteady-state kinetic studies show a facilitated five-step mechanism and provide understanding of how a ring-shaped helicase can be loaded on the DNA during the initiation of replication. The effect of a primase recognition sequence on the observed kinetics suggests that binding to the helicase DNA-binding site is facilitated by transient binding to the primase DNA-binding site, which is proposed to be a loading site. The proposed model involves the fast initial binding of the DNA to the primase site on the outside of the helicase ring, a fast conformational change, a ring-opening step, migration of the DNA into the central channel of the helicase ring, and ring closure. Although an intermediate protein-DNA complex is kinetically stable, only the last species in the five-step mechanism is poised to function as a helicase at the unwinding junction.

Elevation of Vernier thresholds during image motion depends on target configuration

Previously we showed that thresholds for abutting Vernier targets are unaffected by motion, as long as the targets are processed by the same spatial-frequency channel at each velocity and remain equally detectable [Invest. Ophthalmol. Visual Sci. (Suppl.) 37, S734 (1996)]. In this study we compared Vernier thresholds for stationary and moving abutting and nonabutting targets (gaps = 0, 18, and 36 arc min) for velocities of 0-16 deg/s. The Vernier targets were spatially filtered vertical lines (peak spatial frequency = 3.3 or 6.6 c/deg), presented at contrast levels of two, four, and eight times the detection threshold of each component line. Unlike the results for abutting targets, Vernier thresholds for nonabutting targets worsen with velocity as well as gap size. The results for abutting Vernier targets are consistent with the hypothesis that thresholds are mediated by oriented spatial filters, whose responses increase proportionally with the stimulus contrast. The velocity-dependent thresholds found for nonabutting Vernier targets can be explained on the basis of local-sign comparisons if the comparison process is assumed to include a small amount of temporal noise.

DNA binding in the central channel of bacteriophage T7 helicase-primase is a multistep process. Nucleotide hydrolysis is not required

Many helicases assemble into ring-shaped hexamers and bind DNA in their central channel. This raises the question as to how the DNA gets into the central channel to form a topologically linked complex. We have used the presteady-state stopped-flow kinetic method and protein fluorescence changes to investigate the mechanism of single-stranded DNA (ssDNA) binding to the bacteriophage T7 helicase-primase, gp4A'. We have found that the kinetics of 30-mer ssDNA binding to a preformed gp4A' hexamer in the presence of both Mg-dTMP-PCP and Mg-dTTP are similar, indicating that Mg-dTTP binding is sufficient and hydrolysis is not necessary for efficient DNA binding. Multiple transient changes in gp4A' fluorescence revealed a four-step mechanism for DNA binding with Mg-dTTP. These transient changes were analyzed by global fitting and kinetic simulation to determine the intrinsic rate constants of this four-step mechanism. The initial steps, including the bimolecular encounter of the DNA with the helicase and a subsequent conformational change, were fast. We propose that these initial steps of DNA binding occur at a readily accessible site, which is likely to be on the outside of the hexamer ring. The binding of the 30-mer ssDNA at this loading site is followed by slower conformational changes that allow the DNA to transit into the central channel of gp4A' via a ring-opening or threading pathway.

Neuromuscular effects of mivacurium in 2- to 12-yr-old children with burn injury

BACKGROUND

Burned patients are usually resistant to the neuromuscular effects of nondepolarizing relaxants, mostly because of receptor changes. The magnitude of the resistance is related to burn size and time after burn. Mivacurium is a muscle relaxant, degraded by plasma cholinesterase, whose enzyme activity is decreased in burns. The present study tested the hypothesis that burn-induced depressed plasma cholinesterase activity counteracts the receptor-mediated resistance, resulting in a lack of resistance to mivacurium.

METHODS

Burned patients (n = 23), aged 2-12 yr, subclassified into burns of 10-30% or > 30% of body surface, were studied at < or = 6 days and again at 1-12 weeks after burn if possible. Thirteen additional patients served as controls. Neuromuscular variables monitored included onset and recovery following bolus dose, continuous infusion rates required to maintain 95 +/- 4% paralysis, and recovery rates following infusion.

RESULTS

The onset times of maximal twitch suppression were not different between burns and controls, but recovery to 25% of baseline twitch height was prolonged in patients with > 30% burn irrespective of time after injury. The continuous infusion rates to maintain twitch suppression at 95 +/- 4% were not different between groups. The recovery indices, including train-of-four to > 75%, 25-75%, or 5-95% in burned patients, were similar or prolonged compared with controls. The prolonged recovery in burned patients was inversely related to plasma cholinesterase activity (R2 = 0.86, r = -0.93, P < 0.001), and the decreased plasma cholinesterase activity was related to burn size and time after burn.

CONCLUSIONS

A normal mivacurium dosage (0.2 mg/kg) effects good relaxation conditions in burned patients, with an onset time similar to that in controls. This finding contrasts with the response seen with other nondepolarizing drugs, higher doses of which are required to effect paralysis. The decreased metabolism of mivacurium, resulting from depressed plasma cholinesterase activity, probably counteracts the receptor-mediated potential for resistance. Because succinylcholine is contraindicated in burned patients, larger doses of nondepolarizing agents are advocated to effect rapid onset of paralysis. This generalization does not hold for mivacurium. diatrics; plasma cholinesterase; relaxant resistance; succinylcholine, alternative to.)

Nitroglycerin for rapid tocolysis: development of a protocol and a literature review

OBJECTIVE

A protocol for nitroglycerin (NTG) use based on experiences with regard to new and previously described obstetric cases is presented. The efficacy of NTG tocolysis for obstetric emergencies is clinically evaluated.

STUDY DESIGN

Hemodynamically stable parturients requiring acute tocolysis were treated with intravenous NTG and closely monitored. Clinical information was subsequently abstracted from medical records and compared with data from previous reviews.

RESULTS

Tocolytic treatment was successful in all cases (22 of 22, 100%). Complications were clinically insignificant. The most common problem was transient hypotension, which occurred in 9 of 22 (41%) cases.

CONCLUSION

NTG is an effective tocolytic with minimal complications, rapid onset, and a brief half-life. These characteristics favor its use during select obstetric procedures. However, strict adherence to protocols for administration is advised.

The mechanism of ATP hydrolysis at the noncatalytic sites of the transcription termination factor Rho

Escherichia coli transcription termination factor rho is a hexamer with three catalytic subunits that turnover ATP at a fast rate and three noncatalytic subunits that turnover ATP at a relatively slow rate. The mechanism of the ATPase reaction at the noncatalytic sites was determined and was compared with the ATPase mechanism at the catalytic sites. A sequential mechanism for ATP binding or hydrolysis that was proposed for the catalytic sites was not observed at the noncatalytic sites. Pre-steady-state pulse-chase experiments showed that three ATPs were tightly bound to the noncatalytic sites and these were simultaneously hydrolyzed at a rate of 1.8 s(-1) at 18 degrees C. The apparent bimolecular rate constant for ATP binding was determined as 5.4 x 10(5) M(-1) s(-1) in the presence of poly(C) RNA. The ATP hydrolysis products dissociated from the noncatalytic sites at 0.02 s(-1). The hydrolysis of ATP at the noncatalytic sites was at least 130 times slower, and the overall ATPase turnover was 1500 times slower than that at the catalytic sites. These results from studies of the rho protein are likely to be general to hexameric helicases. We propose that the ATPase activity at the noncatalytic site is too slow to drive translocation of the protein on the nucleic acid or to provide energy for nucleic acid unwinding.

The helicase from hepatitis C virus is active as an oligomer

The helicase from hepatitis C virus (HCV NS3h) residing on the C-terminal domain of nonstructural protein 3 was considered to be monomeric by several researchers. Here we demonstrate, based on biochemical kinetic data, that the HCV helicase acts as an oligomer. The increase in the ATPase k(cat) of the NS3h protein with increasing protein concentration provided evidence for oligomerization. A sharp decrease in the unwinding rate was observed when the wild type NS3h was mixed with the ATPase deficient mutants of NS3h protein. This provided strong support for both mixed oligomer formation and subunit interactions for the HCV helicase. Chemical cross-linking of NS3h protein was an inefficient process, but yielded cross-linked protein oligomers of various sizes. The information currently available for HCV helicase is consistent with the hypothesis that oligomers of NS3h are not stable and the helicase subunits exchange during unwinding. Nevertheless, oligomerization of HCV helicase stimulates the ATPase activity, and it is required for the helicase activity.

Nonlinear alteration of transient vergence dynamics after sustained convergence

BACKGROUND

Adaptation models of the horizontal disparity vergence system assume a nonadaptable transient component. They also predict identical postadaptation dynamics during convergence and divergence movements.

METHOD

To test the adaptation property of the transient component, a set of experiments were performed in which closed-loop vergence dynamics measured before and after sustained convergence were compared, primarily by comparing the peak vergence velocity, occurrence time of peak vergence velocity, and steady-state vergence posture. Vergence dynamics after durations of 30, 60, and 90 s of sustained convergence were compared with those after a control duration of 5 s.

RESULTS

The peak divergence velocity was reduced by about 25% within 30 s of sustained vergence. However, the peak convergence velocity was unchanged for all the exposure durations. Additionally, for all durations, the peak divergence velocity was significantly higher than peak convergence velocity. In contrast to peak velocities, the occurrence time of peak convergence and divergence velocity did not differ significantly and remained unchanged for all durations.

CONCLUSIONS

The transient component is adaptable. Furthermore, the adaptation is direction dependent and affects divergence and convergence dynamics differently, thereby suggesting involvement of separate pathways for convergence and divergence in the vergence sensorimotor control.

Vernier judgments in the absence of regular shape information

Vernier acuity is a form of hyperacuity in which the threshold offset between a test object and a reference object is smaller than the size of a foveal cone. Because the test and the reference objects usually have regular shapes (e.g. rectangular, triangular or circular), relatively few studies have addressed the role of shape information in determining hyperacuity thresholds. In this study, we investigated the effect of shape information on hyperacuity performance using targets of irregular shape with different skew and symmetry properties. Vernier thresholds smaller than 10 arc-sec were obtained for closely spaced asymmetric irregular-shape targets. Thresholds for dots and asymmetric irregular shapes increased with increase in center-to-center gap between the targets. Unlike dots, the thresholds for asymmetric irregular shapes also increased with target area. Although the thresholds for asymmetric irregular shapes were higher than those for dots, thresholds for symmetric irregular shapes were similar. Target skew below a certain level had a negligible effect on Vernier thresholds for asymmetric shapes. Our results suggest the existence of feature-independent neural circuitry that can support hyperacuity thresholds and are consistent with the use of the centroid as a primitive for relative localization.

Photopolymer-filled nanoporous glass as a dimensionally stable holographic recording medium

The holographic recording characteristics of a photopolymer-nanoporous-glass composite are reported. An M/# of 3.2 is measured in this medium by angle multiplexing of a series of plane-wave holograms. In addition, the dimensional stability of the material is demonstrated by the negligible Bragg detuning of a set of angle-multiplexed holograms recorded with varying grating tilt angles and by the relative insensitivity of the detuning to changes in temperature.

Transcription termination factor Rho contains three noncatalytic nucleotide binding sites

The active form of transcription termination factor rho from Escherichia coli is a homohexamer, but several studies suggest that the six subunits of the hexamer are not functionally identical. Rho has three tight and three weak ATP binding sites. Based on our findings, we propose that the tight nucleotide binding sites are noncatalytic and the weak sites are catalytic. In the presence of RNA, the rho-catalyzed ATPase rate is fast, close to 30 s-1. However, under these conditions the three tightly bound nucleotides dissociate from the rho hexamer at a slow rate of 0.02 s-1, indicating that the three tight nucleotide binding sites of rho do not participate in the fast ATPase turnover. These slowly exchanging nucleotide binding sites of rho are capable of hydrolyzing ATP, but the resulting products (ADP and Pi) bind tightly and dissociate from rho about 1500 times slower than the fast ATPase turnover. Both RNA and excess ATP in solution are necessary for stabilizing nucleotide binding at these sites. In the absence of RNA, or when solution ATP is hydrolyzed to ADP, a faster dissociation of nucleotides was observed. Based on these results, we propose that the rho hexamer is similar to the F1-ATPase and T7 DNA helicase-containing noncatalytic sites that do not participate in the fast ATPase turnover. We propose that the three tight sites on rho are the noncatalytic sites and the three weak sites are the catalytic sites.

Bacteriophage T7 DNA helicase binds dTTP, forms hexamers, and binds DNA in the absence of Mg2+. The presence of dTTP is sufficient for hexamer formation and DNA binding

The role of Mg2+ in dTTP hydrolysis, dTTP binding, hexamer formation, and DNA binding was studied in bacteriophage T7 DNA helicase (4A' protein). The steady state kcat for the dTTPase activity was 200-300-fold lower in the absence of MgCl2, but the Km was only slightly affected. Direct dTTP binding experiments showed that the Kd of dTTP was unaffected, but the stoichiometry of dTTP binding was different in the absence of Mg2+. Two dTTPs were found to bind tightly in the absence of Mg2+ in contrast to three to four in the presence of Mg2+. In the presence of DNA there was little difference in the stoichiometry of dTTP binding to 4A'. These results indicate that Mg2+ is not necessary for dTTP binding, but Mg2+ is required for optimal hydrolysis of dTTP. Gel filtration of 4A' in the presence of dTTP without Mg2+ showed that Mg2+ was not necessary, and dTTP was sufficient for hexamer formation. The hexamers formed in the presence of dTTP without Mg2+ were capable of binding single-stranded DNA. However, the 4A' hexamers formed in the presence of dTDP with or without Mg2+ did not bind DNA, indicating that hexamer formation itself is not sufficient for DNA binding. The hexamers need to be in the correct conformation, in this case in the dTTP-bound state, to interact with the DNA. Thus, the gamma-phosphate of dTTP plays an important role in causing a conformational change in the protein that leads to stable interactions of 4A' with the DNA.

Acousto-optic random-access laser scanning microscopy: fundamentals and applications to optical recording of neuronal activity

A novel approach to laser scanning microscopy is presented that utilizes diffraction-based scanning principles to achieve fast random-access positioning of a focused laser beam. This non-imaging approach overcomes the speed limitation of present reflection-based scanning microscopes while maintaining high spatial resolution. The presented system combines conventional video microscopy with fast non-imaging scanning microscopy. Together with readily available optical indicators of neuronal activity, this system permits multi-site optical recording from living brain tissue. In this paper, we will review the underlying principles of laser scanning microscopy and the steps in development that led to the current acousto-optic scanning system. We will present typical signals recorded with the current system, and we will outline ongoing extensions of the system. We will also discuss the present limitation of this instrumentation and look into directions of future development.

Increased DNA unwinding efficiency of bacteriophage T7 DNA helicase mutant protein 4A'/E348K

Bacteriophage T7 4A' protein is a DNA helicase that unwinds DNA in a reaction coupled to dTTP hydrolysis. To understand better its mechanism of DNA unwinding, we characterized a set of 4A' mutant proteins (Washington, M. T., Rosenberg, A. H., Griffin, K., Studier, F. W., and Patel, S. S. (1996) J. Biol. Chem. 271, 26825-26834). We showed here, using single turnover DNA unwinding assays, that the 4A'/E348K mutant protein had the unusual property of unwinding DNA (with a 5-6-fold slower rate) despite a significant defect in its dTTPase activity (a 25-30-fold slower rate). Comparing the DNA unwinding rates to the dTTPase rates, we estimated the DNA unwinding efficiencies of both wild-type (about 1 base pair unwound per dTTP hydrolysis) and mutant (4 to 6 base pairs unwound per dTTP hydrolysis). Thus the mutant had a 4-6-fold improvement in its DNA unwinding efficiency over that of the wild-type. We believe that this mutant undergoes less slippage (uncoupled dTTP hydrolysis) than the wild-type. We speculate that nature has selected for a high rate of DNA unwinding rather than a high efficiency of DNA unwinding. Thus even though the mutant is more efficient at DNA unwinding, the wild-type probably was selected because it unwinds DNA faster.