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Biomedical subjects

L I Pizer

Publications and source records attributed to L I Pizer.

At least 73 records · Page 4Linked to original sources
PubMed1971

Biochemical bases for the antimetabolite action of L-serine hydroxamate.

The amino acid analogue l-serine hydroxamate, which is bacteriostatic for Escherichia coli, has been shown to inhibit protein synthesis. The antimetabolite is a competitive inhibitor of seryl-transfer ribonucleic acid (tRNA) synthetase with a K(i) value of 30 mum. Mutants resistant to l-serine hydroxamate have been selected, and three were shown to have seryl-tRNA synthetases with increased K(i) values. One mutant contains a 3-phosphoglycerate dehydrogenase which is insensitive to inhibition by l-serine.

Bacterial Proteins↗
PubMed1969

Phosphatidic acid synthesis in Escherichia coli.

The kinetic properties of acyl-coenzyme A (CoA): l-alpha-glycerol-phosphate trans-acylase (EC 2.3.1.15) from Escherichia coli were studied. At 10 C, a temperature at which the reaction was proportional to time and enzyme concentration, the enzyme had an apparent K(m) of 60 mum for l-alpha-glycerol-phosphate. The curve describing the velocity of the reaction as a function of palmitoyl-CoA concentration was sigmoid but the plot of v(-1) versus [S](-3) gave a straight line. A K(m) of about 11 mum was calculated for palmitoyl-CoA. Adenosine triphosphate specifically inhibited the reaction, being a noncompetitive inhibitor in respect to l-alpha-glycerol phosphate. Inhibition only occurred with high concentrations of palmitoyl-CoA, and maximal inhibition was 60%.

Acyltransferases↗
PubMed1969

Serine biosynthesis and regulation in Haemophilus influenzae.

Nutritional mutants of Haemophilus influenzae requiring l-serine for growth were shown to be deficient in their capacity to synthesize serine-phosphate from 3-phosphoglycerate. On the basis of the correlation between this block and the requirement for an exogenous supply of the amino acid, it was concluded that the "phosphorylated" pathway is the only pathway used by H. influenzae for serine biosynthesis. Serine inhibits serine-phosphate production, thereby regulating its own synthesis in a manner analagous to the Enterobacteriaceae. A mutant strain that required either serine or tryptophan for growth was normal in serine-phosphate synthesis and regulation. It was concluded that this strain probably has a tryptophan synthetase with an increased Michaelis constant for serine.

Carbon Isotopes↗
PubMed1969

Abortive infection of Shigella dysenteriae P2 by T2 bacteriophage.

We have investigated some of the biochemical events that accompany the abortive infection by T2 of Shigella dysenteriae lysogenized with the temperate phage P2. After infection with T2, protein and RNA synthesis continued for 3 to 5 min. The virus-induced enzyme, deoxycytidylate hydroxymethylase was produced in reduced amounts (15% of normal), and the extent of deoxyribonucleic acid (DNA) synthesis was 0.1% of that found with a nonlysogenic strain. Measurements of the production of acid-soluble fragments and sedimentation analyses failed to detect enzymatic degradation of the infecting viral DNA which could be specifically related to the presence of the prophage P2. Each interaction between T2 and a bacterium resulted in the death of the cell. This observation is consistent with results obtained with other types of bacteria which show that only when a nucleolytic attack occurs on T2 DNA does the cell have an increased capacity to survive after adsorption of T2.

Bacteriophages↗
PubMed1968

Effect of prophage W on the propagation of bacteriophages T2 and T4.

Studies have been undertaken to determine whether the temperate phage omega present in Escherichia coli strain W is responsible for the inability of this strain to act as a host for T2 and T4. E. coli WS, cured of phage omega, was sensitive to T2 and T4. Lysogenation of E. coli C and WS with phage omega resulted in loss of ability to plate T2 and T4. However, E. coli K-12 lysogens still served as hosts for the T -even phage. Two of three WS lysogens studied resembled strain W at the biochemical level. They converted about 30% of infecting T2 deoxyribonucleic acid (DNA) to acid-soluble fragments and limited macromolecular synthesis to a few minutes after infection. The third lysogen did not degrade phage DNA, and nucleic acid and protein synthesis continued for some time, although no phage production occurred. It is concluded that phage omega plays a role in the restriction of virulent phage but that it is not the only factor involved. Since acid solubilization was not observed in all cases of phage omega-mediated restriction of T -even phage, a hypothesis for the restriction has been proposed which is based on an alteration in the cell envelope after lysogenation with phage omega.

Coliphages↗
PubMed1968

Phospholipid synthesis in Escherichia coli infected with T4 bacteriophages.

After infection of Escherichia coli with T4 phage, phospholipid synthesis continued but at a reduced rate. The same phospholipid components were synthesized as in uninfected cells; however, the relative rates of (32)P(i) incorporation into phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) were altered. This alteration was most pronounced during the first 10 min after infection. Under these conditions, the isotope incorporated into PG equaled or exceeded that found in PG from uninfected cells. Chloramphenicol (CM) added before, but not 5 min after, infection inhibited the relative increase in PG synthesis, and CM added at different times after infection indicated that a protein synthesized between 3 and 6 min was required for this change to occur. Supplies of exogenous l-serine or l-alpha-glycerol-P failed to affect the relative rates of (32)P(i) incorporation into PG and PE by infected or uninfected cells. Phospholipid synthesis was somewhat higher after infection with T4rII mutants than after infection with wild-type phage. After infection with these mutants or several amber mutants, the relative synthesis of PG and PE was characteristic of T4r(+)-infected cells. The phospholipid synthesized after infection did not rapidly turn over, but infection accelerated the loss of PG synthesized prior to infection.

Autoradiography↗