Joint Theater Trauma System implementation of burn resuscitation guidelines improves outcomes in severely burned military casualties.

BACKGROUND: Between March 2003 and June 2007, our burn center received 594 casualties from the conflicts in Iraq and Afghanistan. Ongoing acute burn resuscitation as severely burned casualties are evacuated over continents is very challenging. To help standardize care, burn resuscitation guidelines (BRG) were devised along with a burn flow sheet (BFS) and disseminated via the new operational Joint Theater Trauma System to assist deployed providers. METHODS: After the BRG was implemented in January 2006, BRF data were prospectively collected in consecutive military casualties with >30% total body surface area (TBSA) burns (BRG Group). Baseline demographic data and fluid requirements for the first 24 hours of the burn resuscitation were collected from the BFS. Percentage full thickness TBSA burns, presence of inhalation injury, injury severity score, resuscitation-related abdominal compartment syndrome, and mortality were collected from our database. Individual charts were reviewed to determine the presence of extremity fasciotomies and myonecrosis. These results were compared with consecutive military casualties admitted during the 2-year- period before the system-wide implementation of the BRG (control group). RESULTS: One hundred eighteen military casualties with burns >30% TBSA were admitted between January 2003 and June 2007, with n = 56 in the BRG group and n = 62 in the control group. The groups were different in age, but similar in %TBSA, %full thickness, presence of inhalation injury, and injury severity score. There was no difference in the rate of extremity fasciotomies or the incidence of myonecrosis between groups. CONCLUSIONS: The composite endpoint of abdominal compartment syndrome and mortality was significantly lower in the BRG group compared with the control group (p = 0.03). Implementation of the BRG and system-wide standardization of burn resuscitation improved outcomes in severely burned patients. Utilization of the joint theater trauma system to implement system-wide guidelines is effective and can help improve outcomes.

Propagation of allosteric changes through the catalytic-regulatory interface of Escherichia coli aspartate transcarbamylase.

Each of two previously isolated strains of Escherichia coli containing a single nonsense codon within the pyrB gene was suppressed with four different nonsense suppressors. The kinetic analysis using crude extracts of these nonsense-suppressed strains indicated that the mutant aspartate transcarbamylases had altered cooperativity and affinity for aspartate as judged by the substrate concentration at half of the maximal velocity. Both pyrB genes were cloned and then sequenced. In both cases, a single base change was identified which converted a glutamine GAC codon into a TAC nonsense codon. Both mutations occurred in the catalytic chain of aspartate transcarbamylase and were identified at positions 108 and 246. The glutamine at position 108 in the wild-type structure is located at the interface between the catalytic and regulatory chains and is involved in a number of interactions with backbone and side chains of the regulatory chain. The glutamine at position 246 in the wild-type structure is located in the 240s loop of the enzyme. Two additional mutant versions of aspartate transcarbamylase were created by site-directed mutagenesis to further investigate the 108-position in the structure, a glutamine to tyrosine substitution at position 108 of the catalytic chain, and an asparagine to glycine change at position 113 of the regulatory chain, a residue which interacts directly with glutamine-108 in the wild-type structure. Both mutant enzymes have reduced affinity for aspartate. However, the Tyr-108 mutant enzyme exhibits a reduced Hill coefficient while the Gly-113 enzyme exhibits an increased Hill coefficient. The response to the allosteric effectors ATP and CTP is also changed for both the mutant enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between domain closure and binding, catalysis, and regulation in Escherichia coli aspartate transcarbamylase.

Previous evidence, from both crystallographic and biochemical studies, has indicated that profound tertiary and quaternary changes in the structure of Escherichia coli aspartate transcarbamylase occur upon the binding of the bisubstrate analogue N-(phosphonoacetyl)-L-aspartate (PALA). In particular, within a single catalytic polypeptide chain, the aspartate binding domain relocates closer to the carbamyl phosphate binding domain, thereby resulting in a major reorganization of the interface between the two domains. Among the new interactions, salt bridges between Glu-50 and both Arg-167 and Arg-234 are formed. In the present study, site-directed mutagenesis is used to replace Glu-50 by glutamine in the catalytic chain. The Michaelis constant for aspartate of the mutant catalytic subunit is about 10-fold higher and the turnover number 10-fold lower than their respective counterparts in the wild-type catalytic subunit, whereas the dissociation constant for carbamyl phosphate is almost unchanged. For the holoenzyme, this substitution results in an 8-fold decrease in the specific activity, a 20-fold increase in the aspartate concentration that gives half of the maximal velocity, and a loss of cooperativity for both substrates. However, the mutant enzyme is not "frozen" in a low-affinity-low-activity conformation since PALA stimulates the activity severalfold and induces an increase in the sulfhydryl reactivity analogous to that of the wild-type enzyme. Together these results indicate that the stabilization of the aspartate binding domain near the carbamyl phosphate binding domain, through specific interdomain bridging interactions, is necessary for the high-affinity-high-activity configuration of the active site.(ABSTRACT TRUNCATED AT 250 WORDS)