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Biomedical subjects

T E Smith

Publications and source records attributed to T E Smith.

At least 91 records · Page 5Linked to original sources
PubMed1981

Properties of a mutant Escherichia coli phosphoenolpyruvate carboxylase deficient in coregulation by intermediary metabolites.

Phosphoenolpyruvate carboxylase of Escherichia coli is activated by three different mechanisms: contiguous by acetyl coenzyme A, precursor by fructose 1,6-bisphosphate, and compensatory feedback by cytidine 5'-diphosphate (CDP). Even though each activator can interact independently with the enzyme, synergistic effects are observed with some combinations, namely, fructose 1,6-bisphosphate or CDP (coregulators), with acetyl coenzyme A. A mutant was isolated that has a phosphoenolpyruvate carboxylase which is refractory to activation by fructose, 1,6-bisphosphate and CDP. The mutant enzyme was shown to be active primarily as the dimer and to lack cooperativity in substrate binding. The binding of acetyl coenzyme A and substrate, however, was essentially the same as that of the wild-type enzyme. The mutant cells grew extremely slowly on glucose alone as the sole carbon source. The only defect in the mutant appeared to be the inability of this enzyme to be activated by the coregulators. These data are consistent with the thesis that coregulation by fructose 1,6-bisphosphate or CDP is an essential requirement for the activation in vivo of this enzyme.

Carboxy-Lyases↗
PubMed1980

Escherichia coli phosphoenolpyruvate carboxylase. Studies on the mechanism of synergistic activation by nucleotides.

Kinetic studies were done to obtain a quantitative estimation of the synergistic interactions that occur between phosphoenolpyruvate carboxylase (orthophosphate:oxaloacetate carboxylase (phosphorylating) E.C. 4.1.1.31) from Escherichia coli K12 and various combinations of its primary substrate, P-enolpyruvate, and the activators acetylcoenzyme A, CDP, GTP, and fructose 1,6-bisphosphate. The analysis involves the evaluation of apparent K values, KS for P-enolpyru;ate and KA for activators, as a function of the concentration of P-enolpyruvate or another activator in the case of KA determinations. Methods are presented which allow the determination of dissociation constants for P-enolpyruvate and activators from binary, ternary, and quaternary complexes of enzyme with substrates or activators, or both. It was observed that synergistic activation occurs with acetyl coenzyme A and all of the coactivators but not with fructose 1,6-bisphosphate and the other co-activators. The enhancement of binding from the binary enzyme substrate (or activator) complex to the ternary or quaternary complexes is in the range of 100-fold. The dissociation constants for P-enolpyruvate, acetyl coenzyme A, CDP, and fructose 1,6-bisphosphate are the same from any active enzyme species. Synergistic activation by multiple activators reflects the ability of co-activators to shift the equilibrium concentrations of active enzyme species away from the inactive forms via a modified "cascade" scheme, thus decreasing the probability that dissociation of any one activator will yield an inactive enzyme species.

Acetyl Coenzyme A↗
PubMed1976

The nasal bony dorsum and cartilaginous vault. Pitfalls in management.

Our literature is replete with technical descriptions of rhinoplasty techniques designed to avoid certain complications. Analysis of 153 secondary rhinoplasties indicates that no procedure is immune to undesirable results and no specific technique can be employed to manage all potential problems. Critical scrutiny of these cases both preoperatively and intraoperatively indicated a decided recurrence of certain complications in the nasal bony dorsum and cartilaginous vault. Fifty-eight defects of the bony dorsum were encountered. These defects included open vault, wide dorsum, asymmetry, excessive or inadequate hump removal, abnormal nasofrontal angle, step deformities, and bony irregularities. Defects in the cartilaginous middle third of the nose occurred 91 times. These consisted to supratip prominence, valve collapse, asymmetry, and saddle deformity.

Humans↗