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The inactivation of native enzymes by a neutral proteinase from rat intestinal muscle.

ABSTRACT: 1. The solubilization and partial purification of a proteinase from the intestinal smooth muscle of rats fed on protein-free diets are described. 2. It has a mol.wt. of about 33000 and it is stable over a narrow pH range. 3. From its susceptibility to known modifers of proteolytic enzymes, it appears to be a serine proteinase of a trypsin-like nature. Active-site titration with soya-bean trypsin inhibitor shows that the concentration of proteinase was about 3 microgram/g wet wt. of intestinal smooth muscle. However, the muscle proteinase demonstrates a marked ability for inactivating enzymes in their native conformation at neutral pH. It is about 100 times more efficient than pancreatic trypsin when the inactivating activities are compared on an approximately equimolar basis. 4. Inactivation of the substrate enzymes is accompanied by limited proteolysis, as demonstrated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 5. An endogenous inhibitor was separated from the proteinase by fractionation with (NH4)2SO4. 6. Contamination of the muscle tissue by lumen, mucosal or blood proteinases and inhibitors is shown to be unlikely. 7. A role for the neutral trypsin-like proteinase in initiating the degradation of intracellular enzymes is considered.

SUBMITTER: Beynon RJ

PROVIDER: S-EPMC1185773 | biostudies-other | 1978 Jul

REPOSITORIES: biostudies-other

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Project description: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.

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The inactivation of native enzymes by a neutral proteinase from rat intestinal muscle.

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