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D Mantle

Publications and source records attributed to D Mantle.

102 records · Page 6Linked to original sources
PubMed1985

Purification and characterization of two Cl- -activated aminopeptidases hydrolysing basic termini from human skeletal muscle.

Two aminopeptidases (I and II), hydrolysing basic termini, were purified to homogeneity (as judged by polyacrylamide gel electrophoresis) from human quadriceps muscle by anion-exchange chromatography and preparative electrophoresis. The electrophoretic migration rate of II was approximately 80% of that of I. Both enzymes had the following properties: optimum activity was at pH 6.5; addition of 0.15 M Cl- or Br- anions resulted in a 20-fold or 10-fold increase in activity respectively. There was little or no increase in activity on the addition of other anions, or divalent cations (0.05-5mM). Approximately 50% inhibition of activity was obtained in the presence of bestatin (0.1 microM), rho-hydroxymercuriphenylsulphonic acid (0.1 microM), EDTA (10 mM), 1,10-phenanthroline (100 microM), N-ethylmaleimide (1 mM) and But-Thr-Phe-Pro (0.5 mM). The molecular mass was 72 000 Da (gel filtration). Only the arginyl and lysyl 7-amino-4-methylcoumarin (Amc) derivatives were appreciably hydrolysed; approximate Km values for the reaction of I and II with these substrates (10-250 microM) were estimated as follows: Arg-Amc, KmI = 70 microM, KmII = 270 microM; Lys-Amc KmI = 280 microM, KmII = 400 microM. Both enzymes hydrolysed dipeptides with Arg or Lys as the NH2-terminal amino acid, however this was not an absolute requirement for dipeptide hydrolysis. The action of I and II on physiologically active oligopeptides was very restricted, with only bradykinin, proangiotensin and neurotensin being appreciably degraded. The breakdown of these peptides did not occur by classical aminopeptidase action (i.e. hydrolysis of the NH2-terminal residues), but via cleavage of internal peptide bonds. These results suggest that I and II may be isoenzymes of a Cl- -requiring, thiol-type aminopeptidase, which hydrolyses basic termini. These enzymes may act primarily as dipeptidases, with a very restricted mode of action in the degradation of naturally occurring oligopeptides.

Aminopeptidases↗
PubMed1985

Purification and characterization of a neuropeptide-degrading aminopeptidase from human brain.

The major aminopeptidase from human post-mortem brain (occipital cortex) was purified to homogeneity (as judged by polyacrylamide gel electrophoresis) by anion-exchange chromatography (two steps) and gel filtration (two steps). The molecular weight of the enzyme was estimated as 105,000 from gel filtration. Maximum activity was obtained in the presence of 0.5 mM Ca2+ and 1 mM 2-mercaptoethanol at pH 7.3. Enzyme activity was lost on freezing and thawing or on lyophilization. The enzyme was inhibited by metal-ion chelating agents, sulphydryl blocking agents, bestatin, and puromycin. A series of amino acyl-7-amido-4-methylcoumarins was hydrolysed by the enzyme, with the alanyl derivative being hydrolysed most rapidly (Km 170 microM). Specificity studies with a series of alanine dipeptides suggested that a hydrophobic second residue favoured hydrolysis. Several naturally occurring neuropeptides, including Leu5-enkephalin (Km 180 microM), cholecystokinin octapeptide, and Arg8-vasopressin, were hydrolysed by the aminopeptidase. In a series of opioid peptides, increasing chain length led to decreased susceptibility to hydrolysis. Sulphation of the Tyr1 residue of Leu5-enkephalin and the Tyr2 residue of cholecystokinin octapeptide made the peptides more resistant to hydrolysis.

Aminopeptidases↗
PubMed1983

Purification and characterization of the major aminopeptidase from human skeletal muscle.

The major aminopeptidase from human quadriceps muscle was purified (as judged by polyacrylamide-gel electrophoresis) by anion-exchange chromatography (two steps) and gel filtration (two steps). The enzyme showed maximum activity at pH 7.3, in the presence of 1 mM-2-mercaptoethanol and 0.5 mM-Ca2+ ions; activation of the enzyme occurred in the presence of several other bivalent cations. Inhibition of activity was obtained in the presence of metal-ion-chelating agents and inhibitors of aminopeptidases and thiol proteinases. The molecular weight of the enzyme was 102 000 (by gel filtration). The enzyme hydrolysed several amino acyl-7-amido-4-methylcoumarin derivatives; highest activity was obtained with alanyl-7-amido-4-methylcoumarin. The enzyme also degraded a series of dipeptides, alanine oligopeptides and some naturally occurring peptides. Of particular interest was the high activity of the enzyme towards the enkephalins.

Aminopeptidases↗
PubMed1982

Peroxidase-like activities of iron(III)-porphyrins: kinetics of the reduction of a peroxidatically active derivative of deuteroferriheme by phenols.

The kinetics of reduction of a peroxidatically active intermediate (formed by reaction of deuteroferriheme with hydrogen peroxide) by phenol and a series of substituted phenols have been studied by stopped-flow spectrophotometry. The complex effects of varying heme concentration have been interpreted in terms of the formation of a dimeric form of the intermediate by reaction of monomeric intermediate with unoxidized ferriheme monomer. Both the relative reactivity of phenols towards the two forms of the intermediate and the rate constants for reduction of intermediate are markedly influenced by phenol substituents. Effects of pH suggest that phenolate anions are the reactive forms of the reductants. Rate constants for the monomeric intermediate reactions (kDFH) are related to those (kHRP) for the corresponding reductions of horseradish peroxidase Compound I by the following relation: log kDFH = 1.53 log kHRP -3.74.

Heme↗
PubMed1981

Polymeric structure of pig small-intestinal mucus glycoprotein. Dissociation by proteolysis or by reduction of disulphide bridges.

Pig small-intestinal mucus glycoprotein, of molecular weight 1.72 X 10(6), is cleaved by Pronase digestion into glycoprotein subunits of molecular weight 4.5 X 10(5). Of the protein component of the native glycoprotein 29% by weight was lost on Pronase digestion, with no loss of carbohydrate. The non-glycosylated region of the protein that was lost with proteolytic digestion had a broad spectrum of amino acid residues, in contrast with the glycosylated region of the protein, which was resistant to proteolysis and was rich in serine, threonine and proline residues. Reduction with 0.2M-mercaptoethanol dissociated the Pronase-digested glycoprotein subunits into smaller glycoprotein subunits of molecular weight 2.7 X 10(5). On reduction, the native glycoprotein was dissociated into subunits of molecular weight 2.4 X 10(5), a similar size to those obtained from reduction of the Pronase-digested glycoprotein. On reductive dissociation of the native glycoprotein, in addition to glycoprotein subunits, protein was also released principally as a component of 90000 molecular weight. This protein was separated quantitatively from the reduced glycoprotein in amounts compatible with one 90000-mol.wt. protein molecule per 1.72 X 10(6)-mol.wt. native glycoprotein molecule. No 90000-mol.wt. protein was released on reduction of the isolated Pronase-digested glycoprotein. Pig small-intestinal mucus glycoprotein is therefore a covalent polymer of glycoprotein subunits joined by disulphide bridges. This polymeric structure differs in important respects from that previously shown for gastric mucus, in particular with respect to the size and number of component subunits per native molecule.

Amino Acids↗
PubMed1979

A study of sexual offenses against females.

The objective of this study was to obtain information on sexual offenses against females. Data were obtained from 103 females in two university classes. Eighty-four percent reported having been the victim of a sexual offense. The offenses experienced were obscene telephone calls (61%), sexual molestation (44%), exhibitionism (27%), being followed (24%), attempted rape (16%) and rape (1%). Most offenses were discussed with friends while very few were reported to parents, police or social workers.

Adaptation, Psychological↗
PubMed1977

Hydroperoxidase activities of ferrihemes: heme analogues of peroxidase enzyme intermediates.

By reaction of deuteroferriheme (DFH) with peroxo acids, spectroscopically distinct and peroxidatically active deuteroferriheme-peroxide compounds (DPC) are formed. These species closely resemble, and are probably identical with, the species formed by reaction of DFH with H2O2, which has previously been considered to be an analogue of peroxidase compound I. Stopped-flow spectrophotometric titration studies imply: (a) that DPC is formed by reaction of 1.9 +/- 0.2 mol of DFH with 1 mol of peroxo acid; (b) that the spectral change accompanying formation of DPC is independent of the peroxo acid oxidant used. Titration of the oxidizing power of DPC formed with H2O2 implies that submaximal yields of DPC are obtained, a result that could implicate DPC species as analogues of catalase compound I in the catalase action of ferrihemes. Preliminary results suggest that DPC may involve both monomeric and dimeric heme components.

Catalase↗
PubMed1976

The kinetics of formation of horseradish peroxidase compound I by reaction with peroxobenzoic acids. pH and peroxo acid substituent effects.

1. The kinetics of formation of horseradish peroxidase Compound I were studied by using peroxobenzoic acid and ten substituted peroxobenzoic acids as substrates. Kinetic data for the formation of Compound I with H2O2 and for the reaction of deuteroferrihaem with H2O2 and peroxobenzoic acids, to form a peroxidatically active intermediate, are included for comparison. 2. The observed second-order rate constants for the formation of Compound I with peroxobenzoic acids decrease with increasing pH, in the range pH 5-10, in contrast with pH-independence of the reaction with H2O2. The results imply that the formation of Compound I involves a reaction between the enzyme and un-ionized hydroperoxide molecules. 3. The maximal rate constants for Compound I formation with unhindered peroxobenzoic acids exceed that for H2O2. Peroxobenzoic acids with bulky ortho substituents show marked adverse steric effects. The pattern of substituent effects does not agree with expectations for an electrophilic oxidation of the enzyme by peroxoacid molecules in aqueous solution, but is in agreement with that expected for a reaction involving nucleophilic attack by peroxo anions. 4. Possible reaction mechanisms are considered by which the apparent conflict between the pH-effect and substituent-effect data may be resolved. A model in which it is postulated that a negatively charged 'electrostatic gate' controls access of substrate to the active site and may also activate substrate within the active site, provides the most satisfactory explanation for both the present results and data from the literature.

Benzoates↗
PubMedDate not supplied

Estimation of tyrosine by the attenuation of 4-iodophenol enhanced chemiluminescence.

Tyrosine markedly attenuates the chemiluminescence output intensity from the 4-iodophenol enhanced chemiluminescence assay system in a manner consistent with competition between the amino acid and luminol for the 4-iodophenoxy radical. This effect provides the basis for a sensitive assay of tyrosine. Interference by the other amino acids has been assessed; major interference by cysteine can be removed by incubation with iodoacetic acid.

Chloromercuribenzoates↗
PubMedDate not supplied

Specificity of action of human brain alanyl aminopeptidase on Leu-enkephalin and dynorphin-related peptides.

The major cystosolic aminopeptidase (alanylaminopeptidase) was purified to homogeneity from human cerebral cortex and the specificity of its actions on a series of Leu-enkephalin-related peptides of increasing chain length was determined. In each case, only the N-terminal Tyr-Gly bond was hydrolysed. Kinetic analysis of the data revealed that the specificity constant (kcat/Km;s-1M-1) falls with increasing chain length from a maximum of 13.6 x 10(4) for Leu-enkephalin (5 residues) to 5.8 x 10(2) for dynorphin (1-13). Dynorphin 1-17, while not being degraded itself acted as a competitive inhibitor (Ki = 2.7 microM) of the degradation of smaller peptides. Beta-endorphin was not hydrolysed by analylaminopeptidase, nor did it act as an inhibitor of the enzyme.

Aminopeptidases↗