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Biomedical subjects

T K Ray

Publications and source records attributed to T K Ray.

At least 73 records · Page 4Linked to original sources
PubMed1976

Studies on the phosphorylated intermediates of a K+-stimulated ATPase from rabbit gastric mucosa.

A density gradient-purified microsomal membrane preparation from rabbit fundic gastric mucosa was used for a detailed study of the K+-stimulated ATPase and associated intermediate reactions. Membranes incubated with gamma-[32P]ATP show the rapid incorporation of 32P into phosphoprotein. Phosphoprotein levels were markedly reduced (1) when ATP hydrolysis went to completion or (2) upon addition of unlabeled ATP, thus suggesting the participation of a rapid turnover phosphorylated intermediate in the gastric microsomal ATPase. Addition of K+, Rb+ or Tl+ greatly reduced the level of the intermediate while stimulating ATPase activity; the observed affinities of these cations were similar for the effects on both ATPase and intermediate levels, with Tl+ greater than K+ greater than Rb+. Neither ATPase nor intermediate were stimulated by Na+, and ouabain was without effect on the reactions, thus differentiating this system from the (Na+ + K+)-ATPase. Addition of various inhibitors showed differential effects on the partial reactions of the gastric ATPase system. N-ethylmaleimide and Zn2+ showed characteristics of completely abolishing the K+-stimulated component of ATPase as well as the effects of K+ in reducing the level of intermediate, thus suggesting that these agents exert their inhibitory effect on a phosphoprotein phosphatase partial reaction. F- abolished the K+-stimulated ATPase, but its more complex effects on the intermediate suggested an additional reaction step within the domain of the phosphorylated intermediate. Results are consistent with a model system for the gastric microsomal ATPase involving a Mg2+-dependent protein kinase, a phosphorylated intermediate(s), and a K+-stimulated phosphoprotein phosphatase.

Adenosine Diphosphate↗
PubMed1976

Activation of long chain fatty acids with acyl carrier protein: demonstration of a new enzyme, acyl-acyl carrier protein synthetase, in Escherichia coli.

A soluble enzyme activity which catalyzes the synthesis of acyl-acyl carrier protein from acyl carrier proteins, a long chain fatty acid, and ATP has been demonstrated in E. coli. The reaction requires high concentrations of both Ca++ and Mg++ for activity, and cleaves ATP to AMP and PPi. The fatty acyl product has been identified as acyl-acyl carrier protein by its solubility, thioester linkage, molecular weight, charge, and biological activity. Several criteria indicate the enzyme is distinct from acyl-CoA synthetase. The fatty acid specificity of the enzyme suggests a role of acyl-acyl carrier protein synthetase in the incorporation of fatty acids into phospholipid.

Adenosine Triphosphate↗
PubMed1976

Specific inhibition of phospholipid synthesis in plsA mutants of Escherichia coli.

plsA mutants of Escherichia coli are temperature-sensitive strains which possess two enzymes of abnormal thermolability, sn-glycerol 3-phosphate acyltransferase and adenylate kinase. Phospholipid synthesis is inhibited after shift of plsA mutants to temperatures at the lower end of the nonpermissive temperature range. This inhibition is not due to inactivation of the adenylate kinase activity since nucleic acid (and hence adenosine 5'-triphosphate) synthesis is inhibited only slightly. These results show that in vivo inactivation of the sn-glycerol 3-phosphate acyltransferase can be observed under conditions which allow normal adenylate kinase function.

Acyltransferases↗
PubMed1975

Acylation of sn-glycerol 3-phosphate in Escherichia coli. Study of reaction with native palmitoyl-acyl carrier protein.

The sn-glycerol-3-phosphate acyltransferase activity of Escherichia coli has been assayed using native palmitoyl-acyl carrier protein as the acyl donor. This substrate was synthesized by a plant chloroplast system which utilized E. coli acyl carrier protein. The properties of the acyltransferase as assayed with palmitoyl-acyl carrier protein were similar to those observed using palmitoyl-CoA as the acyl donor. This finding suggested that single enzyme catalyzed transfer of acyl groups from either thioester to sn-glycerol 3-phosphate. This hypothesis was tested by assay of two classes of E. coli mutants which have altered sn-glycerol-3-phosphate acyltransferases. Both classes (plsA and plsB) of mutants have similarly altered activities as assayed with either palmitoyl-acyl carrier protein or palmitoyl-CoA. These results indicate that the same acyltransferase enzyme (or enzyme system) catalyzes the incorporation of both thioester substrates into phospholipid. Other experiments have shown that the acyltransferase of a plsB mutant was abnormally thermolabile only when palmitoyl-CoA was the acyl donor in the reaction. No thermolability was observed with palmitoyl-acyl carrier protein as acyl donor. The thermolability observed with palmitoyl-CoA is attributed to the detergent properties of this substrate. In agreement with Lueking and Goldfine (Lueking, D. R., and Goldfine, H. (1975) J. Biol. Chem. 250, 4911-4917), we found that guanosine-5'-diphosphate-3'-diphosphate (ppGpp) inhibits the acyltransferase only when palmitoyl-CoA was the acyl donor. No inhibition was observed when the acyltransferase was assayed with palmitoyl-acyl carrier protein in the presence of ppGpp. Incubation of the enzyme with ppGpp to assay results in a profound inhibition of acyltransfer from palmitoyl-CoA but has no effect on the incorporation of acyl groups from palmitoyl-acyl carrier protein.

Acyltransferases↗
PubMed1970

Selection and characterization of an E. coli mutant defective in membrane lipid biosynthesis.

A procedure is described for the selection of temperature-sensitive phospholipid mutants based upon radiation suicide of the wild-type organisms by tritiated L-glycerol-3-phosphate incorporated in the phospholipids. One of these mutants possesses an acyltransferase activity much more thermolabile than that of its parent. This mutant ceases growth and phospholipid biosynthesis immediately upon shift to a nonpermissive temperature although DNA, RNA, and protein continue to be synthesized. The phenotype of this mutant appears due to a single mutation by reversion analysis and by enzymatic analysis of temperature-resistant revertants.

Cell Membrane↗