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L I Pizer

Publications and source records attributed to L I Pizer.

At least 55 records · Page 3Linked to original sources
PubMed1975

Regulatory properties of purified 3-phosphoglycerate dehydrogenase from Bacillus subtilis.

3-Phosphoglycerate dehydrogenase (3-phosphoglycerate:NAD oxidoreductase, EC. 1.1.1.95) was purified from Bacillus subtilis by conventional methods. The final preparation was homogeneous by electrophoretic analysis and had a sedimentation constant of 6.3 S. On the basis of gel filtration data the enzyme had a molecular weight of about 166000. The plot of velocity versus phosphoglycerate concentration was biphasic while similar plots for hydroxypyruvate phosphate and NADH were the conventional hyperbolic type. The enzyme was specifically inhibited by serine. The inhibition was time dependent, requiring several minutes incubation before a constant level of inhibition was achieved. Serine inhibition was of the "mixed type" with respect to 3-phosphoglycerate and Hill plots of these data had slopes that approached 2. Desensitization of the enzyme to serine inhibition was achieved by incubation in the absence of dithiothreitol. The desensitized enzyme was different from the native enzyme in fluoresence properties, sedimentation characteristics and in the absence of the biphasic phosphoglycerate saturation curve. Evidence was obtained for the participation of sulphydryl groups in the changes in protein structure responsible for serine inhibition as well as the dehydrogenase activity of the enzyme.

Alcohol Oxidoreductases↗
PubMed1974

Regulation of one-carbon biosynthesis and utilization in Escherichia coli.

The regulation of several enzymes involved in one-carbon metabolism was studied in a mutant of Escherichia coli K-12 defective in S-adenosylmethionine synthetase. The mutant that was reported to have a low endogenous concentration of S-adenosylmethionine had elevated levels of N-5, 10-methylene tetrahydrofolate reductase and serine transhydroxymethylase, but the level of N-5, 10-methylene tetrahydrofolate dehydrogenase was not altered. These results suggest that S-adenosylmethionine plays a role in the regulation of one-carbon production and utilization. An enzyme system that cleaved glycine to one-carbon units was demonstrated. The enzymes responsible for the cleavage of glycine were induced by exogenous glycine but were independent of S-adenosylmethionine or purine levels in the cell.

Adenine↗
PubMed1973

Effect of serine hydroxamate on phospholipid synthesis in Escherichia coli.

Serine hydroxamate, which inhibits the charging of seryl-transfer ribonucleic acid, reduced the synthesis of phospholipid and nucleic acids in Escherichia coli. This effect was analogous to depriving amino acid auxotrophs of their nutritional requirement and appears to be a manifestation of the stringent response shown by rel(+) strains of E. coli. Amino acid starvation (serine or methionine) alone or serine hydroxamate treatment alone results in 60 to 80% inhibition of lipid accumulation, 90% inhibition of ribonucleic acid accumulation, and an increase in guanosine tetraphosphate (ppGpp). These three effects were reversed by addition of chloramphenicol (CM). A combination of serine starvation and serine hydroxamate treatment resulted in inhibition of lipid and RNA accumulation as well as an increase in ppGpp, but the consequences of the double block were not reversed by CM. We conclude that a strong interrelationship exists among these processes and that CM acts to relax a stringent response by mechanisms other than interference with ppGpp formation. All species of phospholipid were affected by a stringent response evoked by amino acid starvation or addition of serine hydroxamate, but in all cases the synthesis of phosphatidylethanolamine was most severely inhibited. Serine hydroxamate was not incorporated into lipid but specifically caused phosphatidylserine accumulation. Serine starvation produced a dramatic alteration of the distribution of isotope incorporated into phospholipid, which resulted from the stringent response compounded with the limitation of a substrate for phosphatidylserine synthesis.

Adenosine Triphosphate↗
PubMed1973

Regulation of phospholipid synthesis in Escherichia coli by guanosine tetraphosphate.

Phospholipid synthesis has been reported to be subject to stringent control in Escherichia coli. We present evidence that demonstrates a strict correlation between guanosine tetraphosphate accumulation and inhibition of phospholipid synthesis. In vivo experiments designed to examine the pattern of phospholipid labeling with (32)P-inorganic phosphate and (32)P-sn-glycerol-3-phosphate suggest that regulation must occur at the glycerol-3-phosphate acyltransferase step. Assay of phospholipid synthesis by cell-free extracts and semipurified preparations revealed that guanosine tetraphosphate inhibits at least two enzymes specific for the biosynthetic pathway, sn-glycerol-3-phosphate acyltransferase as well as sn-glycerol-3-phosphate phosphatidyl transferase. These findings provide a biochemical basis for the stringent control of lipid synthesis as well as regulation of steady-state levels of phospholipid in growing cells.

Acetyltransferases↗
PubMed1973

Enzymatic defects in three genetic classes of serine-requiring mutants of Bacillus pumilus.

Serine-requiring mutants of Bacillus pumilus NRRL B-3275 have been divided into three groups based on the position of the mutant loci on the linkage map of this organism. Representatives of each group were found deficient in enzymatic activities that constitute the phosphorylated pathway for serine biosynthesis. The evidence suggests that the genes coding for the enzymes of the phosphorylated pathway of serine biosynthesis are not clustered in B. pumilus.

Bacillus↗
PubMed1972

Serine biosynthesis and its regulation in Bacillus subtilis.

Cell-free extracts of Bacillus subtilis strains GSY and 168 convert (14)C-phosphoglycerate to (14)C-serine phosphate and (14)C-serine. These reactions indicate a functional phosphorylated pathway for serine biosynthesis in these cells. The addition of serine to the incubation mixture inhibited the formation of both radioactive products. Extracts of mutant strains that require serine for growth lacked the capacity to synthesize serine phosphate, confirming that the phosphorylated pathway was the only functional pathway available for serine synthesis. Serine phosphate phosphatase and phosphoglycerate dehydrogenase activity were demonstrated in cell extracts, and the phosphoglycerate dehydrogenase was shown to be inhibited specifically by l-serine. The extent of serine inhibition increased when the temperature was raised from 25 to 37 C, and the thermal stability of the enzyme was enhanced by the presence of the inhibitor serine or the coenzyme reduced nicotinamide adenine dinucleotide. At 37 C the curve representing the relationship between phosphoglycerate concentration and enzyme velocity was biphasic, and the serine inhibition which was competitive at low substrate concentrations became noncompetitive at higher concentrations.

Ammonium Sulfate↗
PubMed1971

Effect of trimethoprim on macromolecular synthesis in Escherichia coli.

Trimethoprim is a specific inhibitor of dihydrofolate reductase. When added to amino acid supplemented cultures of Escherichia coli, protein, ribonucleic acid (RNA), and deoxyribonucleic acid synthesis are rapidly inhibited. It is shown that thymidylate and purine synthesis must continuously occur if the inhibition is to be maintained. These results are interpreted as demonstrating that in vivo trimethoprim can reduce but not totally inhibit the action of dihydrofolate reductase and therefore reduce the amount of tetrahydrofolate derivatives available for formylmethionyl transfer RNA formylation, purine, and thymidylate synthesis.

Adenine↗
PubMed1971

Effect of serine hydroxamate on the growth of Escherichia coli.

The structural analogue of l-serine, l-serine hydroxamate, inhibited the growth of Escherichia coli K-12. Of the other amino acid hydroxamates tested, only l-lysine hydroxamate reduced the rate of growth. Inhibition of growth by l-serine hydroxamate was rapidly reversed by the addition of l-serine to the bacterial culture or by removal of the analogue by filtration. The reversal of inhibition was specific for l-serine. l-Alanine, glycine, or adenine had no effect on an inhibited culture. No evidence for active transport of the analogue was obtained.

Adenine↗