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Biomedical subjects

I T Carney

Publications and source records attributed to I T Carney.

7 recordsLinked to original sources
PubMed1984

A kinetic model for the action of the enzyme activated irreversible inhibitor 4-amino-5-hexynoic acid in vivo.

The extent of inactivation of three aminotransferases by the enzyme activated inhibitor 4-amino-hex-5-ynoate (acetylenic-GABA) increased with increasing dose in an exponential fashion. Theoretical treatment of the data allowed an estimate of the effective concentration of the drug at its site of action to be made and it was apparent that any rises in substrate concentration produced by the inactivation did not protect the enzyme significantly. Altered diet produced distinct changes in the extent of inactivation of aspartate aminotransferase, but not with ornithine aminotransferase. Cysteine sulphinate, a substrate only of aspartate aminotransferase, also affected the inactivation of ornithine aminotransferase, suggesting that secondary metabolic effects were responsible.

4-Aminobutyrate Transaminase↗
PubMed1980

A low-molecular-weight inhibitor of the neutral proteinase from rat intestinal smooth muscle.

1. Rat intestinal smooth muscle was shown to contain endogenous inhibitory activity towards the neutral trypsin-like muscle proteinase described previously [Beynon & Kay (1978) Biochem. J. 173, 291--298]. 2. Comtamination of the muscle tissue by mucosal, blood and pancreatic inhibitors was shown to be unlikely. 3. The inhibitory activity was resolved into high- and low-molecular-weight components. 4. The low-molecular-weight component was purified to homogeneity. It has a molecular weight of approx. 9000 and was stable over the pH range 3--11. 5. It inhibited the muscle proteinase competitively (Ki congruent to t microM), but had no effect on any of the other proteinases tested. 6. Leupeptin also inhibited the muscle proteinase competitively (Ki congruent to 0.3 microM), whereas the low-molecular weight proteins gastrin, glucagon and insulin B-chain had very little effect. 7. A role for a weakly binding inhibitor in modulating the influence of the neutral proteinase on intracellular protein degradation is considered.

Amino Acids↗
PubMed1978

The susceptibility of muscle phosphorylases a and b to digestion by a neutral proteinase from rat intestinal muscle. Comparison with the effects produced by pancreatic trypsin and chymotrypsin.

1. Phosphorylase b was inactivated three times more rapidly than phosphorylase a by a neutral, trypsin-like proteinase from rat intestinal muscle. Digestion of phosphorylase a produced a modified form which was deactivated by AMP. Removal of the pyridoxal phosphate cofactor increased the rate of inactivation of the b form by about 3-fold but the subceptibility of apophosphorylase a was no different from the holo form. 2. The extent of proteolysis of both holoenzyme forms, as guaged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, was limited and similar digestion patterns were obtained in both cases. 3. With (32)P-labelled phosphorylase a as substrate, the initial event in the inactivation was the release of a trichloroacetic acid-soluble peptide from the N-terminus of the enzyme, leaving the original 100000 subunit form essentially unchanged. Subsequent proteolysis was restricted, producing derivatives of mol.wt. 85000, 70000 and 65000, none of which contained any radioactive label. 4. By treatment of inactivated phosphorylase b with carboxypeptidase B, it was shown that the intestinal muscle proteinase had cleaved approximately 3 -Lys-X and 3 -Arg-X bonds in the polypeptide. 5. The protective effects of various allosteric modulators of phosphorylase on the inactivation of the a and b forms were generally in agreement with the known roles of the modifiers. Glucose increased the susceptibility of phosphorylase a. 6. Inactivation of phosphorylase b by trypsin and chymotrypsin also resulted in limited proteolysis but, in both cases, the digestion patterns obtained on sodium dodecyl sulphate/polyacrylamide gels were different from each other and from the pattern obtained with the intestinal muscle proteinase. 7. Inactivation of phosphorylase b by the muscle proteinase is about 100 times more rapid than the effects produced by trypsin or chymotrypsin when the activities are compared on an equimolar basis. 8. Consideration is given to regulation of the rate of enzyme degradation intracellularly by modulation of the conformation and susceptibility of the enzyme via factors such as covalent modification, allosteric ligands and state of aggregation.

Adenosine Monophosphate↗
PubMed1977

The susceptibility of glycogen phosphorylase to inactivation by endogenous and exogenous proteases.

Phosphorylases a and b were inactivated very rapidly by a neutral, trypsin-like protease from rat intestinal muscle. With 32P-phosphorylase a as substrate, it was shown that the initial event in the inactivation was the release of a small, phosphopeptide from the N-terminus of the enzyme, leaving the original 100,000 subunit form virtually unchanged. Subsequent proteolysis was very limited, producing 85, 70 and 65,000 mol. wt. derivatives. The effects of several allosteric modulators of phosphorylase on the rates of inactivation of the two enzymes were studied. Removal of the pyridoxal phosphate cofactor from phosphorylase increased the susceptibility of the b form by three fold while the a form was unaffected. By comparison of these effects with those obtained from digestion with trypsin and chymotrypsin, it is concluded that the intestinal muscle protease has a markedly enhanced ability for inactivating enzymes in their native conformation. Assuming that this property is reflected in vivo, a possible role such neutral proteases in initiating protein degradation is advanced.

Animals↗