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Biomedical subjects

R L Soffer

Publications and source records attributed to R L Soffer.

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

Pulmonary angiotensin-converting enzyme. Structural and catalytic properties.

Angiotensin-converting enzyme has been solubilized from a particulate fraction of rabbit lung and purified to apparent homogeneity in 11% yield by a procedure including fractionation with DEAE-cellulose and calcium phosphate gel, elution from Sephadex G-200, and lectin affinity chromatography. The molecular weight estimated by equilibrium sedimentation was approximately 129,000, either in the absence or presence of 6 M guanidine hydrochloride. A slightly higher value of 140,000 determined for the reduced, denatured protein by gel electrophoresis in the presence of sodium dodecyl sulfate and a much higher figure derived from gel filtration are probably due to the glycoprotein nature of the enzyme. Its oligosaccharide content accounted for 26% of the weight calculated from its amino acid and carbohydrate composition. The estimated content of sugar residues per mole was: galactose, 57; N-acetylglucosamine, 53; mannose, 43; N-acetylneuraminic acid, 19; and fucose, 4. Threonine and alanine were identified, respectively, as NH2-terminal and COOH-terminal residues by the dansylation procedure and by digestion with carboxypeptidase A. The enzyme was found to contain approximately 1 g atom of zinc per mol. Km values for hydrolysis of hippurylhistidylleucine and angiotensin I were 2.3 and 0.07 mM, and the corresponding turnover numbers were 15,430 and 792 mol/min/mol at 37 degrees. Bradykinin was also a substrate, and release of its COOH-terminal dipeptide, Phe-Arg, was catalyzed at a comparable rate to that of His-Leu from the COOH terminus of angiotensin I. Enzyme activity required the presence of chloride ions and was inhibited by EDTA and by low concentrations of Bothrops bradykinin-potentiating peptides. In addition, hydrolysis of hippurylhistidylleucine was inhibited competitively by other defined peptides, including di- and tripeptides, which were not substrates.

Amino Acids↗
PubMed1975

Enzymatic arginylation of beta-melanocyte-stimulating hormone and of angiotensin II.

Porcine beta-melanocyte-stimulating hormone and angiotensin II were examined as acceptors in the reaction catalyzed by arginyl-tRNA-protein transferase. Both inhibited enzymatic transfer of [14C]arginine from tRNA to bovine albumin. Inhibition was competitive with albumin and the K-i values were, respectively, 15 and 0.8 muM. The expected arginylated compounds were isolated and characterized. Beta-melanocyte-stimulating hormone and its arginylated product had identical activities in the frog epithelium bioassay. In contrast, the biological activity of angiotensin II was diminished by enzymatic arginylation. The pressor effect of the arginylated derivative on anesthetized rats and its activity on the isolated rat uterus were, respectively, approximately 60% and 20% of those found for the unmodified peptide.

Acyltransferases↗
PubMed1975

Regulation of proline catabolism by leucyl,phenylalanyl-tRNA-protein transferase.

A mutant of Escherichia coli lacking leucyl,phenylalanyl-tRNA:protein leucyltransferase, EC 2.3.2.6) exhibited several abnormal growth characteristics relative to the wild type or a revertant when grown with glycerol as a carbon source. All three strains were auxotrophic for proline. The mutant required higher levels of this amino acid than did the other strains to attain a normal growth yield and metabolized exogenous [14C]proline more rapidly. The greater rate of proline utilization was associated with a 4-fold increase in specific activity of proline oxidase. When glucose rather than glycerol was employed as a carbon source, proline oxidase activity was reduced by catabolite repression and the growth ccharacteristics of the mutant were similar to those of the parental and revertant strains. These results suggest that the mutant growth phenotype is due to an altered rate of proline catabolism and constitue evidence for regulation of a specific metabolic pathway by leucyl,phenylalanyl-tRNA-protein transferase.

Acyltransferases↗
PubMed1974

A mutant of Escherichia coli defective in leucyl, phenylalanyl-tRNA-protein transferase.

A mutant of E. coli that lacks leucyl,-phenylalanyl-tRNA-protein transferase (EC 2.3.2.6) has been isolated. Ability to produce the two activities could be introduced into the mutant from an F' strain whose episome contains genetic material located between 45 and 54 min on the E. coli chromosome. When grown into stationary phase and resuspended in minimal medium with glycerol, the mutant exhibited a marked lag before resuming growth. Revertants that did not show this lag were selected and were found to have regained both transfer activities. Extracts of wild-type, mutant, and revertant strains were compared as acceptors for the enzymatic transfer of radioactive phenylalanine. Analysis of the labeled polypeptides by disc gel electrophoresis indicated that certain potential acceptors may be preferentially acylated in vivo. These data provide genetic confirmation that the same enzyme protein catalyzes the transfer of leucine and phenylalanine and suggest that leucyl,phenylalanyl-tRNA-protein transferase is involved in a growth regulatory mechanism.

Acyltransferases↗
PubMed1974

Angiotensin-converting enzyme from rabbit pulmonary particles.

Angiotensin-converting enzyme has been solubilized from rabbit pulmonary particles and purified to homogeneity. The molecular weight of the native enzyme was estimated to be about 136,000 by glycerol gradient centrifugation, and a value of 140,000 was obtained for the reduced denatured protein by disc-gel electrophoresis in the presence of sodium dodecyl sulfate and 2-mercaptoethanol. The enzyme was found to be a glycoprotein with carbohydrate accounting for approximately 16% of its dry weight. The major sugar residues were identified as galactose, N-acetylglucosamine, and mannose, with smaller amounts of fucose and sialic acid. The homogeneous enzyme catalyzed the release of His-Leu from the COOH-terminus of angiotensin I and of Phe-Arg and Ser-Pro from that of bradykinin.

Angiotensin II↗
PubMed1971

Modification of a specific ribosomal protein catalyzed by leucyl, phenylalanyl-tRNA: protein transferase.

Escherichia coli ribosomes washed with 1 M NH(4)Cl were found to function as acceptor for leucine and phenylalanine in the reaction catalyzed by leucyl, phenylalanyl-tRNA:protein transferase. When isolated subunits were acylated with [(14)C]phenylalanine and reisolated by gradient centrifugation, the recovered 30S particles had a specific radioactivity nearly 30 times that of similarly treated 50S particles. Autoradiography of gels, which contained protein from acylated 30S particles, that had been subjected to electrophoresis in 8 M urea and in sodium dodecyl sulfate, suggested that acceptor activity was largely due to a single protein with a molecular weight of about 12,000. Leucine and phenylalanine residues that had been transferred to ribosomal protein were reactive with fluorodinitrobenzene and were released as leucyl- or phenylalanylarginine after treatment with trypsin. The results indicate that leucyl, phenylalanyl-tRNA: protein transferase catalyzes the addition of these amino acids to an NH(2)-terminal arginine residue of a specific ribosomal protein on the 30S subunit.

Acyltransferases↗