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Biomedical subjects

Y Shechter

Publications and source records attributed to Y Shechter.

At least 127 records · Page 7Linked to original sources
PubMed1977

Effect of oxidation of methionine residues in chicken ovoinhibitor on its inhibitory activities against trypsin, chymotrypsin, and elastase.

Oxidation of methionine residues of chicken ovoinhibitor with N-chlorosuccinimide resulted in a selective loss of its inhibitory activities. While trypsin inhibiting activity was not affected at all, half of the chymotrypsin-inhibiting activity and all of the elastase inhibiting activity were lost. Electrophoretic and affinity chromatography studies indicated that the 50% loss of the chymotrypsin-inhibiting activity resulted from the inactivation of one of its two chymotrypsin-inhibiting sites rather than from a decrease in the binding constants of both sites. Oxidation of ovoinhibitor-chymotrypsin and ovoinhibitor-elastase complexes with excess of N-chlorosuccinimide indicated that the complex formation in each case protected the site that binds the enzyme which participated in the complex, but did not protect the site that binds the other enzyme. Quantitative estimation of the number of oxidized methionine residues in the ovoinhibitor isolated from the complexes has shown that in each complex about one methionine residue was protected from oxidation. Nitrophenyl-sulfenylation of the single tryptophan residue of ovoinhibitor did not affect its inhibitory activities at all.

Animals↗
PubMed1976

Selective chemical cleavage of tryptophanyl peptide bonds by oxidative chlorination with N-chlorosuccinimide.

Tryptophanyl peptide bonds are selectively cleaved by N-chlorosuccinimide (NCS) under acidic conditions. All other peptide bonds are resistant to cleabage by this reagent. Optimal conditions for cleavage are: 2 equiv of NCS, pH 4-5, or 50-80% acetic acid for 30 min at room temperature. Under these conditions methionine residues are oxidized to methionine sulfoxides and cysteine. Other amino acids are not modified. The cleavage reaction was studied with several peptides containing tryptophan residueas successfully applied to several proteins. In alpha-lactalbumin, Kunitz trypsin inhibitor ,and apomyoglobin, selective cleavage of the expected tryptophanyl peptide bonds was obtained in 19-58% yield. The glucagon molecule was fragmented into two peptides in 32% yield.

Amino Acid Sequence↗
PubMed1976

Lipoprotein lipase in rat lung. Effect of dexamethasone.

The effect of hormone administration on the activity of lipoprotein lipase in the lung was studied in the rat. The following hormones were administered: dexamethasone, L-thyroxine, estradiol-17beta and progesterone. In addition, lung lipoprotein lipase activity was studied in diabetic and lactating rats. Lipoprotein lipase activity was measured in dried, defatted preparations of rat lung using double labeled ([14C]palmitate, [3H]glycerol) chylomicron triacylglycerol as substrate. Dexamethasone administration caused a rise of 70% in the level of activity of lipoprotein lipase in acetone powders of lung and a 100% increase in the amount of enzyme released during heparin infusion into isolated, perfused lungs. Enzyme activity was higher in lungs of females than of male rats; however; the level of activity was unaffected by estrogen or progesterone administration to either male or ovariectomized rats. Diabetes, hyperthyroidism or lactation did not change lipoprotein lipase activity in the lung. The constant presence of lipoprotein lipase activity in the lung suggests that this organ is able to maintain a steady supply of triacylglycerol-fatty acids under a variety of physiological and pathological conditions. Stimulation of enzyme activity by dexamethasone could lead to increased uptake of triacylglycerol-fatty acids by the lung and may thus be a contributing factor to corticosteroid-induced enhanced surfactant synthesis.

Animals↗
PubMed1975

Selective oxidation of methionine residues in proteins.

Methionine residues in peptides and proteins were oxidized to methionine sulfoxides by mild oxidizing reagents such as chloramine-T and N-chlorosuccinimide at neutral and slightly alkaline pH. With chloramine-T cysteine was also oxidized to cystine but no other amino acid was modified; with N-chlorosuccinimide tryptophans were oxidized as well. In peptides and denaturated proteins all methionine residues were quantitatively oxidized, while in native proteins only exposed methionine residues could be modified. Extent of oxidation of methionine residues was determined by quantitative modification of the unoxidized methionine residues with cyanogen bromide (while methionine sulfoxide residues remained intact), followed by acid hydrolysis and amino acid analysis. Methionine was determined as homoserine and methionine sulfoxide was reduced back to methionine. Sites of oxidation were identified in a similar way by cleaving the unoxidized methionyl peptide bonds with cyanogen bromide, followed by quantitative end-group analysis of the new amino-terminal amino acids (by an automatic sequencer).

Amino Acid Sequence↗
PubMed1975

Modulation of the enzymic activity of chicken pepsin by the covalent modification of its single -- SH group.

The single cysteinyl residue of chicken pepsin was modified with a wide spectrum of reagents to produce mixed disulfides or alkylated derivatives. All these derivatives showed enhanced catalytic activity towards the synthetic peptide Z-Ala-Ala-Phe-OPrP, where OPrP is the 3-(4-pyridyl)-propyl-1-oxy group. The overall catalytic constant kcat/Km for these derivatives was 4 -- 25-fold larger than that of the native enzyme. The activity of the enzyme towards denatured hemoglobin was slightly decreased (10--45%) by these modifications. When the mixed disulfide derivatives were treated with excess mercaptan, the sulfhydryl group was regenerated and activity reverted to that of the native enzyme. The --SH group of chicken pepsin reacted preferentially with reagents containing an aromatic group. The reaction was found to depend on the ionization of a single group, presumably the --SH itself, with a pKa = 7.5. The rate of reaction of the fully deprotonated species with various disulfides was 100--1000-fold smaller than that of the --SH group of glutathione. It is suggested that the groups attached covalently to the sulfhydryl also interact with other amino acid side chains in the protein thereby affecting the active center of chicken pepsin.

Amino Acids↗