Mild Traumatic Brain Injury and Career Stage Associate with Visible Perivascular Spaces in Special Operations Forces Soldiers

Mild traumatic brain injury (mTBI) and occupational blast exposure in military Service Members may lead to impaired brain waste clearance which increases neurological disease risk. Perivascular spaces (PVS) are a key part of the glymphatic system which supports brain waste clearance, preferentially during sleep. Visible PVS on clinical magnetic resonance imaging have been previously observed in patients with neurodegenerative diseases and animal neurotrauma models. The purpose of this study was to determine associations between PVS morphological characteristics, military career stage, and mTBI history in Special Operations Forces (SOF) Soldiers. Participants underwent T2-weighed neuroimaging to capture three-dimensional whole brain volumes. Segmentation was performed using a previously validated, multi-scale deep convolutional encoder-decoder neural network. Only PVS clusters within the white matter mask were quantified for analyses. Due to non-normal PVS metric distribution, non-parametric Mann-Whitney U tests were used to determine group differences in PVS outcomes. In total, 223 healthy SOF combat Soldiers (age = 33.1 ± 4.3yrs) were included, 217 reported career stage. Soldiers with mTBI history had greater PVS number (z = 2.51, P = 0.013) and PVS volume (z = 2.42, P = 0.016). In-career SOF combat Soldiers had greater PVS number (z = 2.56, P = 0.01) and PVS volume (z = 2.28, P = 0.02) compared to a baseline cohort. Mild TBI history is associated with increased PVS burden in SOF combat Soldiers that are clinically recovered from mTBI. This may indicate ongoing physiological changes that could lead to impaired waste clearance via the glymphatic system. Future studies should determine if PVS number and volume are meaningful neurobiological outcomes for neurodegenerative disease risk and if clinical interventions such as improving sleep can reduce PVS burden.

Mild traumatic brain injury history is associated with lower brain network resilience in soldiers

Special Operations Forces combat soldiers sustain frequent blast and blunt neurotrauma, most often classified as mild traumatic brain injuries. Exposure to repetitive mild traumatic brain injuries is associated with persistent behavioural, cognitive, emotional and neurological symptoms later in life. Identifying neurophysiological changes associated with mild traumatic brain injury exposure, in the absence of present-day symptoms, is necessary for detecting future neurological risk. Advancements in graph theory and functional MRI have offered novel ways to analyse complex whole-brain network connectivity. Our purpose was to determine how mild traumatic brain injury history, lifetime incidence and recency affected whole-brain graph theoretical outcome measures. Healthy male Special Operations Forces combat soldiers (age = 33.2 ± 4.3 years) underwent multimodal neuroimaging at a biomedical research imaging centre using 3T Siemens Prisma or Biograph MRI scanners in this cross-sectional study. Anatomical and functional scans were preprocessed. The blood-oxygen-level-dependent signal was extracted from each functional MRI time series using the Big Brain 300 atlas. Correlations between atlas regions were calculated and Fisher z-transformed to generate subject-level correlation matrices. The Brain Connectivity Toolbox was used to obtain functional network measures for global efficiency (the average inverse shortest path length), local efficiency (the average global efficiency of each node and its neighbours), and assortativity coefficient (the correlation coefficient between the degrees of all nodes on two opposite ends of a link). General linear models were fit to compare mild traumatic brain injury lifetime incidence and recency. Nonparametric ANOVAs were used for tests on non-normally distributed data. Soldiers with a history of mild traumatic brain injury had significantly lower assortativity than those who did not self-report mild traumatic brain injury (t148 = 2.44, P = 0.016). The assortativity coefficient was significantly predicted by continuous mild traumatic brain injury lifetime incidence [F1,144 = 6.51, P = 0.012]. No differences were observed between recency groups, and no global or local efficiency differences were observed between mild traumatic brain injury history and lifetime incidence groups. Brain networks with greater assortativity have more resilient, interconnected hubs, while those with lower assortativity indicate widely distributed, vulnerable hubs. Greater lifetime mild traumatic brain injury incidence predicted lower assortativity in our study sample. Less resilient brain networks may represent a lack of physiological recovery in mild traumatic brain injury patients, who otherwise demonstrate clinical recovery, more vulnerability to future brain injury and increased risk for accelerated age-related neurodegenerative changes. Future longitudinal studies should investigate whether decreased brain network resilience may be a predictor for long-term neurological dysfunction.

Warfighter Resilience

PURPOSE

Our aim in this study was to psychometrically test resilience assessments (Ego Resiliency Scale [ER89], Connor-Davidson Resilience Scale [CD-RISC 25], Responses to Stressful Experiences Scale [RSES short-form]) and describe resilience levels in a Special Operations Forces (SOF) combat sample.

METHODS

Fifty-eight SOF combat Servicemembers either entering SOF (career start; n = 38) or having served multiple years with their SOF organization (mid-career; n = 20) self-reported resilience, mild traumatic brain injury (mTBI) history, and total military service.

RESULTS

All resilience metrics demonstrated acceptable internal consistency, but ceiling effects were found for CD-RISC and RSES scores. ER89 scores were moderate on average. ER89 scores were higher in SOF career start than mid-career Servicemembers (ηρ2 = 0.07) when accounting for the interaction between SOF career stage and total military service (ηρ2 = 0.07).

DISCUSSION

SOF mid-career Servicemembers had similar ER89 resilience scores with more total military service. The SOF career start combat Servicemembers had higher ER89 measured resilience with less total military service only, potentially showing a protective effect of greater service before entering SOF.

CONCLUSION

The ER89 may be a more optimal military resilience metric than the other metrics studied; longitudinal research on SOF combat Servicemember resilience is warranted.

Relationship between Anterior Pituitary Volume and IGF-1 Serum Levels in Soldiers with Mild Traumatic Brain Injury History

PURPOSE

A high mild traumatic brain injury (mTBI) incidence rate exists in military and sport. Hypopituitarism is an mTBI sequela; however, few studies have examined this phenomenon in those with an mTBI history. This cross-sectional study of Special Operations Forces combat soldiers aimed 1) to relate anterior pituitary gland volumes (actual and normalized) to insulin-like growth factor 1 (IGF-1) concentrations, 2) to examine the effect of mTBI history on anterior pituitary gland volumes (actual and normalized) and IGF-1 concentrations, and 3) to measure the odds of demonstrating lower anterior pituitary gland volumes (actual and normalized) or IGF-1 concentrations if self-reporting mTBI history.

METHODS

Anterior pituitary gland volumes were manually segmented from T1-weighted 3D brain MRI sequences; IGF-1 serum concentrations were quantified using commercial enzyme-linked immunosorbent assays. Correlations and linear regression were used to determine the association between IGF-1 serum concentration and anterior pituitary gland volume (n = 74). Independent samples t-tests were used to compare outcomes between mTBI groups and logistic regression models were fit to test the odds of demonstrating IGF-1 concentration or anterior pituitary volume less than sample median based on mTBI group (n = 54).

RESULTS

A significant linear relationship between the subjects' anterior pituitary gland volumes and IGF-1 concentrations (r72 = 0.35, P = 0.002) was observed. Soldiers with mTBI history had lower IGF-1 concentrations (P < 0.001) and lower anterior pituitary gland volumes (P = 0.037) and were at greater odds for IGF-1 serum concentrations less than the sample median (odds ratio = 5.73; 95% confidence interval = 1.77-18.55).

CONCLUSIONS

Anterior pituitary gland volume was associated with IGF-1 serum concentrations. Mild TBI history may be adversely associated with anterior pituitary gland volumes and IGF-1 concentrations. Longitudinal IGF-1 and anterior pituitary gland monitoring may be indicated in those who report one or more mTBI.

Active Warfighter Mental Health Lower in Mid-Career

PURPOSE

The present study investigated Special Operations Forces (SOF) combat Servicemember mental health at different SOF career stages in association with resilience.

METHODS

Fifty-eight SOF combat Service Members either entering SOF (career start; n=38) or multiple years with their SOF organization (mid-career; n=20) self-reported mild traumatic brain injury (TBI) history, resilience, subjective well-being, depression, anxiety, and posttraumatic stress. Poisson regression analyses were employed to test SOF career stage differences in each mental health symptom using resilience, while accounting for other pertinent military factors.

RESULTS

There were significant interaction effects of SOF career stage and resilience on mental health symptoms. SOF career start combat Servicemembers endorsed lower depression and posttraumatic stress and higher subjective well-being with higher resilience, but these associations between resilience and mental health symptoms were not seen in SOF mid-career Servicemembers.

CONCLUSIONS

Although preliminary, the adaptive association between resilience and mental health seemed to be blunted in combat Servicemembers having served multiple years in SOF. This information informs research to provide evaluation tools to support prophylactic performance and long-term health preservation in military populations.

Behavioral health clinicians endorse stellate ganglion block as a valuable intervention in the treatment of trauma-related disorders

The stellate ganglion block (SGB) procedure has been used successfully for over 10 years to treat post-traumatic stress symptoms in thousands of US military service members, civilians, and veterans in select hospitals in Europe and North America. Primarily through targeting the autonomic nervous system, the SGB procedure serves as an invaluable adjunct to trauma-focused psychotherapy. Without published best practices for emerging therapies, clinicians are left on their own to determine how best to apply new treatments to their patient populations. The aim of this qualitative research was to compile attitudes and recommendations from therapists with expertise in using SGB for treating symptoms of post-traumatic stress disorder, so that their experiences could be disseminated widely to clinicians without SGB expertise. An 18-item survey was developed and distributed electronically to a group of behavioral health professionals of various specialties between May and June 2020. Of surveyed behavioral health clinicians with personal experience incorporating SGB into their trauma-focused psychotherapy, 95% of respondents would recommend SGB to a colleague as a useful tool for the treatment of trauma-related disorders. SGB was rated at least as useful as the most valuable interventions listed in the American Psychological Association Clinical Practice Guideline for the Treatment of Post-traumatic Stress Disorder with 100% of respondents characterizing SGB as ‘Very Beneficial’ or ‘Somewhat Beneficial’, and 0 respondents characterizing SGB as ‘Not Helpful’ or ‘Harmful’. Given the feedback from this study, behavioral health providers should consider using SGB in conjunction with standard trauma-focused care.

The relationship between resilience and neurophysiological stress in Special Operations Forces combat service members

Military resilience research is increasing due to the growing literature associating resilience with stress adaptation. This study aimed to investigate which physiological stress adaptation components were associated with resilience in Special Operations Forces combat service members. Special Operations Forces combat service members (n = 117) self-reported resilience (ER89) and lifetime clinician-confirmed mild traumatic brain injury history. Participants also underwent transcranial Doppler ultrasonography to measure middle cerebral artery velocity during rest and a breath-holding task. Neither resilience nor mild traumatic brain injury history was significantly associated with middle cerebral artery velocity percent increase following breath-holding; younger Special Operations Forces combat service members had a higher percent increase in middle cerebral artery velocity following a breath-holding task. Resilience was negatively associated with time to return to baseline middle cerebral artery velocity following peak velocity; whereas, mild traumatic brain injury history did not have a significant association. The Special Operations Forces combat service members that scored higher in resilience tended to return to baseline middle cerebral artery velocity following peak velocity faster than their less resilient counterparts. More resilient Special Operations Forces combat service members recovered faster from physiological stress (breath-holding) than less resilient counterparts. This is the first study to investigate resilience and cerebrovascular stress response and recovery in this population. Our initial findings indicated that the Ego Resiliency Scale may be an optimal resilience psychometric and should be used to evaluate effective military resilience trainings, which aim to improve performance and mental health.

Mental Health Symptoms Are Associated With Mild Traumatic Brain Injury History in Active Special Operations Forces (SOF) Combat and Combat Support Soldiers

INTRODUCTION

Special Operations Forces (SOF) combat arms and combat support Soldiers are at risk for impaired mental health, such as mood- and stress-related disorders, due to operational and training demands. Additionally, these individuals experience high risk for sustaining mild traumatic brain injury (mTBI). These mTBIs have also been linked to negative psychological outcomes, such as anxiety and depressive symptoms. Studying mental illnesses and their related symptoms alone does not fully address mental health, which may be better understood by 2 separate but overlapping continua measuring both mental illness and subjective well-being (ie, emotional, psychological, and social well-being). Due to the lack of research in this area, current mental health symptoms in active SOF combat Soldiers in relation to mTBI warrants investigation.

MATERIALS AND METHODS

In this study, 113 SOF combat and combat support Soldiers completed self-report psychological and mTBI history measures during an in-person laboratory setting. These psychometric measures included (1) psychological distress (Brief Symptom Inventory 18), (2) anxiety (Generalized Anxiety Disorder 7-item), (3) posttraumatic stress (PTSD Checklist for DSM-5), (4) somatization (Patient Health Questionnaire-15), and (5) subjective well-being (Mental Health Continuum Short Form).

RESULTS

On average, SOF combat Soldiers endorsed moderate well-being and low psychological distress, somatization, posttraumatic stress, and anxiety. Most SOF combat Soldiers had sustained 1 or more mTBI. We observed mTBI history had significant effects on each dependent variable in the expected directions. History of more mTBIs, controlling for age, was associated with lower subjective well-being as well as higher psychological distress, somatization, posttraumatic stress, and anxiety symptoms.

CONCLUSION

Although SOF combat Soldiers reported relatively adaptive mental health symptoms across participants, there was considerable variance in the measures reported. Some of the variance in mental health symptoms was accounted for by mTBI history while controlling for age, with reporting higher numbers of lifetime mTBIs and older age being associated with worse mental health symptoms. Longitudinal investigations into these associations and their impact on Soldier performance is warranted.

Effects of Combat Deployment on Anthropometrics and Physiological Status of U.S. Army Special Operations Forces Soldiers

INTRODUCTION

U.S. Army Special Operations Forces (SOF) soldiers deploy frequently and conduct military operations through special warfare and surgical strike capabilities. Tasks required to execute these capabilities may induce physical and mental stress and have the potential to degrade soldier physiological status. No investigations have longitudinally characterized whether combat deployment alters anthropometrics or biochemical markers of physiological status in a SOF population of frequent deployers.

MATERIALS AND METHODS

Effects of modern combat deployment on longitudinal changes in anthropometrics and physiological status of elite U.S. Army SOF soldiers (n = 50) were assessed. Changes in measures of body composition, grip strength, physiological status, and health behaviors from baseline to postdeployment were determined with paired t test and McNemar's statistic. Baseline measures were obtained between 4 and 8 weeks before deployment. Deployment length was a uniform duration of time between 3 and 6 months (all soldiers completed the same length of deployment). Post hoc analyses determined change in body mass within quartiles of baseline body mass with paired t test and associations between change in sex hormone-binding globulin (SHBG) and change in body mass with correlation coefficient. The study was approved by the Human Use Review Committee at the U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts.

RESULTS

In response to deployment, increases in lean mass (77.1 ± 7.6 to 77.8 ± 7.5 kg), maximum grip strength (57.9 ± 7.2 to 61.6 ± 8.8 kg), and conduct of aerobic (156 ± 106 to 250 ± 182 minutes/week) and strength training (190 ± 101 to 336 ± 251 minutes/week) exercise were observed (p < 0.05). Increases in serum SHBG (35.42 ± 10.68 to 38.77 ± 12.26 nmol/L) and decreases in serum cortisol (443.2 ± 79.3 to 381.9 ± 111.6 nmol/L) were also observed (p < 0.05). Body mass changes were dependent on baseline body mass. Soldiers in the lowest quartile of baseline body mass increased body mass (75.6 ± 2.6 vs. 76.6 ± 2.8 kg, p = 0.03), as did those in the second quartile (81.6 ± 2.0 vs. 83.7 ± 3.5 kg, p = 0.02). Those in the third quartile also tended to increase body mass (89.2 ± 2.6 vs. 90.9 ± 3.3 kg, p = 0.05), while those in the upper quartile tended to decrease body mass (98.5 ± 3.6 vs. 96.7 kg, p = 0.06). Change in SHBG was inversely correlated with change in body mass (r = -0.33, p = 0.02). There were no changes in fat mass, body fat percentage, waist circumference, neck circumference, total testosterone, calculated bioavailable or free testosterone, high-sensitivity C-reactive protein, tumor necrosis factor-α, interleukin-1β, or interleukin-6. Inflammatory markers were skewed toward lower values.

CONCLUSIONS

Overall, physiological status of elite SOF soldiers characterized by multiple prior deployments was minimally impacted by combat deployment, in the absence of major unit casualties. The majority experienced some adaptive changes, including increased lean mass, grip strength, time spent engaged in exercise, and decreased levels of the stress hormone cortisol. Mechanisms contributing to inverse correlations between change in SHBG and change in body mass may be further clarified. Future investigations may also more fully characterize the degradation and optimization of health and physiological status of SOF training and deployment cycles with in-theater data collection and repeated measures.

Effects of deployment on diet quality and nutritional status markers of elite U.S. Army special operations forces soldiers

Background

Special Operations Forces (SOF) Soldiers deploy frequently and require high levels of physical and cognitive performance. Nutritional status is linked to cognitive and physical performance. Studies evaluating dietary intake and nutritional status in deployed environments are lacking. Therefore, this study assessed the effects of combat deployment on diet quality and serum concentrations of nutritional status markers, including iron, vitamin D, parathyroid hormone (PTH), glucose, and lipids, among elite United States (U.S.) Army SOF Soldiers.

Methods

Changes from baseline to post-deployment were determined with a repeated measure within-subjects design for Healthy Eating Index-2010 (HEI-2010) scores, intake of foods, food groups, key nutrients, and serum nutritional status markers. Dietary intake was assessed with a Block Food Frequency Questionnaire. The association between post-deployment serum 25-hydroxy vitamin D (25-OH vitamin D) and PTH was determined. Analyses of serum markers were completed on 50 participants and analyses of dietary intake were completed on 33 participants.

Results

In response to deployment, HEI-2010 scores decreased for total HEI-2010 (70.3 ± 9.1 vs. 62.9 ± 11.1), total fruit (4.4 ± 1.1 vs. 3.7 ± 1.5), whole fruit (4.6 ± 1.0 vs. 4.2 ± 1.4), dairy (6.2 ± 2.7 vs. 4.8 ± 2.4), and empty calories (14.3 ± 3.2 vs. 11.1 ± 4.5) (P ≤ 0.05). Average daily intakes of foods and food groups that decreased included total dairy (P < 0.01), milk (P < 0.01), and non-juice fruit (P = 0.03). Dietary intake of calcium (P = 0.05) and vitamin D (P = 0.03) decreased. PTH increased from baseline (3.4 ± 1.6 vs. 3.8 ± 1.4 pmol/L, P = 0.04), while there was no change in 25-OH vitamin D. Ferritin decreased (385 ± 173 vs. 354 ± 161 pmol/L, P = 0.03) and soluble transferrin receptor increased (16.3 ± 3.7 vs. 17.1 ± 3.5 nmol/L, P = 0.01). There were no changes in glucose or lipids. Post-deployment, serum 25-OH vitamin D was inversely associated with PTH (r = −0.43, P < 0.01).

Conclusions

HEI-2010 scores and dietary intake of milk, calcium, and vitamin D decreased following deployment. Serum PTH increased and iron stores were degraded. No Soldiers were iron deficient. Personnel that deploy frequently should maintain a high diet quality in the U.S. and while deployed by avoiding empty calories and consuming fruits, vegetables, and adequate sources of calcium, vitamin D, and iron. Improving availability and quality of perishable food during deployment may improve diet quality.

Structural changes accompanying human serum albumin's binding of fatty acids are concerted

Long chain fatty acids (LCFAs), a major source of cellular energy, are solubilized and transported in the blood by binding to serum albumin. Changes in human serum albumin's (HSA's) UV absorption and characteristic reactivity with pyridoxal-5'-phosphate appear to reflect a concerted change in its structure upon binding five equivalents of myristate. Isothermal titrations with myristate and other LCFA anions are also consistent with the presence of five strong, interacting, binding sites. Although HSA is usually thought to have many independent LCFA anion binding sites, just five interacting sites appear to account for the changes in structure that accompany its binding of myristate.

Reactions of acrylamide with glutathione and serum albumin

Rate constants of 0.0054 and 0.021 M(-1)s(-1) for the reactions of acrylamide with human serum albumin (HSA) and glutathione (GSH), respectively, were determined under physiological conditions by following the loss of their thiol groups in the presence of excess acrylamide. Based on these in vitro values, reactions with these thiols appear to account for most of acrylamide's elimination from the body. Combined with data from other studies, these results should be useful for assessing the health risk of dietary acrylamide.

5-Nitrosothio-2-nitrobenzoate: a reagent for the nitrosation of thiol groups in proteins

The S-nitroso derivative of 5-thio-2-nitrobenzoate was synthesized from 5,5'-dithiobis(2-nitrobenzoic acid) and partially characterized. Although relatively unstable, it is easy to prepare and reacts very rapidly with thiols and thiol groups of proteins to give corresponding S-nitrosothiols and 5-thio-2-nitrobenzoate dianion. The latter's easy spectrophotometric detection makes such reactions easy to follow and to quantitate.

S-nitrosation of serum albumin: spectrophotometric determination of its nitrosation by simple S-nitrosothiols

The transfer of nitroso groups from S-nitroso-L-cysteine (1) and six other simple S-nitrosothiols to Cys 34 of bovine serum albumin (2) has been followed using Ellman's reagent, 5,5'-dithio-bis (2-nitrobenzoate) (3), to detect the resulting thiols. The described method utilizes the low reactivity of (3) with (2) and the high extinction coefficient of 2-nitro-5-thiobenzoate produced upon its reaction with thiols to follow the transfer of nitroso moieties at low concentrations where other procedures are not feasible. A second-order rate constant of 6400 M-1 s-1 obtained for the reaction of (2) with S-nitrosomercaptoethylamine is approximately 10 times faster than that for its reaction with (1), approximately 40 times faster than that for its reaction with S-nitrosoglutathione, and consistent with Cys 34 being located in a narrow crevice in close proximity to an anionic charge.

A procedure for the determination of monothiols in the presence of dithiothreitol--an improved assay for the reduction of disulfides

4,4'-Dipyridyl disulfide (4-PDS) and sodium arsenite have been used to develop a rapid and sensitive assay for monothiols in the presence of dithiothreitol (DTT). The procedure is similar to that of Zahler and Cleland (J. Biol. Chem. 243, 716-719, 1968) but involves the use of a lower pH and 4-PDS, which is more effective than 5,5'-dithiobis-(2-nitrobenzoic acid) at low pH. Background reactions that interfere with the determination of slow reacting thiol groups are much reduced in the new assay procedure. The reduction of oxidized glutathione by DTT at three different pH values and a partial and the complete reduction of bovine serum albumin by DTT have been characterized in order to demonstrate the use of this procedure. In the first two cases monothiol groups were readily detected without interference from DTT. Lower than expected numbers of thiol groups in the case of three reduced and denatured model proteins appeared to reflect their partial complexation by arsenite. Equilibrium and kinetic constants for the formation and dissociation of the DTT-arsenite complex from pH 5 to 8 are presented.

Transnitrosation as a predominant mechanism in the hypotensive effect of S-nitrosoglutathione

S-Nitrosoglutathione, a possible intermediate in the pharmacological mechanisms of many vasodilators, undergoes hemolysis at pH 7.4 and 37 degrees C to give oxidized glutathione and nitric oxide with a second-order rate constant of approximately 3 x 10(-4) M-1sec-1. At the dosages normally employed, this reaction is, therefore, too slow to be an obligatory step in the pharmacological mechanisms of those, usually, fast-acting drugs. Transfers of the nitroso moiety to another thiol or to certain hemoproteins are, however, both much faster and could be involved in those pharmacological mechanisms. Intravenously administered S-nitrosoglutathione reduced the blood pressure of anesthesized dogs and monkeys to the same extent and with essentially the same rapid onset and dissipation as sodium nitroprusside, which is the fastest-acting of those vasodilators.

The reactivity of p-nitrophenyl acetate with serum albumins

1. Serum albumins from nine of 10 vertebrate species were found to react rapidly with p-nitrophenylacetate. 2. The high reactivities were shown to be partially attributable to strong, rapidly reversible binding of p-nitrophenylacetate by each serum albumin. 3. As previously observed in the case of human serum albumin (Koh and Means, Arch. Biochem. Biophys. 192, 73-79, 1979), this binding takes place in the primary binding site for several physiologically (i.e. tryptophan, small fatty acid anions) and pharmacologically (i.e. diazepam) important compounds. 4. Horse serum albumin differed from all other serum albumins included in this study in that it did not react rapidly with p-nitrophenylacetate, presumably, due to significant differences in its corresponding binding site.

Inactivation of angiotensin converting enzyme by sodium nitroprusside

Angiotensin I converting enzyme is rapidly inactivated by sodium nitroprusside and that inactivation is suppressed in the presence of chloride ion and by the presence of L-alanyl-L-proline or glycyl-L-tryptophan, which are both competitive inhibitors of its catalytic activity. The inactivation by sodium nitroprusside appears to result from the modification of an unusually reactive lysine residue in or near the active site.

Trypsin inactivation by intact Hymenolepis diminuta (Cestoda): some characteristics of the inactivated enzyme

In the presence of intact Hymenolepis diminuta, trypsin was inactivated; intact worms had no apparent effect on subtilisin, pepsin, or papain. Inactivation of trypsin was demonstrable using azoalbumin as a substrate, but the inactivated enzyme retained full catalytic activity against benzoyl-DL-arginine-p-nitroanilide, p-tosyl-L-arginine methyl ester (low molecular weight synthetic trypsin substrates) and p-nitro-p-guanidinobenzoate (an active site titrant). Inactivation was not reversible under conditions of heating, freezing and thawing, or prolonged dialysis of the enzyme. Analyses of inactivated 3H-trypsin by cationic and SDS-polyacrylamide gel electrophoresis, and gel chromatography failed to indicate the presence of a high molecular weight trypsin inhibitor associated with the inactivated enzyme; no low molecular weight, dissociable inhibitor was demonstrable following thermal denaturation of the inactivated enzyme. Analyses of trypsin after incubation in the presence of pulse-labeled worms also failed to demonstrate the presence of any inhibitor of worm origin associated with the inactivated enzyme. The data suggest that inactivation is the result of a small structural or conformational change in the enzyme molecule, a change which partially (rather than totally) inactivates the enzyme towards protein substrates.

Stabilization of bovine trypsin by reductive methylation

Reductive methylation has little or no detectable effect on the catalytic or physicochemical properties of bovine trypsin but reduces its susceptibility to autolysis. Increased stability after methylation appears to result from the conversion of trypsin-susceptible lysine residues to trypsin-resistant epsilon-N,N-dimethyllysine residues. Reductively methylated trypsin is easily prepared and may be useful in place of trypsin where autolysis is otherwise difficult to control.

Acetylation of human serum albumin by p-nitrophenyl acetate

Human serum albumin reacts very rapidly with p-nitrophenyl acetate (NphOAc). Rapid acetylation of the protein accompanies and largely accounts for the easily observed rapid formation of of p-nitrophenolate ion. One group is acetylated much faster than all others. It appears to be located in a high affinity binding site for small fatty acid anions, to have a pKa of 8.7, and a limiting bimolecular rate of reaction with NphOAc of approximately 3 X 10(4) M-1 sec-1 at alkaline pH values. Rapid reversible binding appears to be a major contributor to the high reaction velocity.