title: The reversible thiol-disulphide exchange of trypsin and chymotrypsinogen with a tumour-derived inhibitor. Kinetic data obtained with fluorescein-labelled polymeric collagen fibrils and casein as substrates.
abstract: Ehrlich ascites cells contain a cytoplasmic inhibitor of both trypsin and the granule neutral protease and possess a reactive thiol which interacts with an important disulphide bond in trypsin, resulting in the formation of the trypsin-inhibitor complex. When a fixed quantity of trypsin was completely inhibited by addition of the cytoplasmic inhibitor, the trypsin could be re-activated by the addition of either trasylol-trypsin or chymotrypsinogen. Since trasyloltrypsin, chymotrypsinogen (and any derived chymotrypsin) has no ability to solubilise fluorescein-labelled peptides from the substrate, the appearance of trypsin activity was probably due to a non-enzymic exchange reaction, in which these inactive forms displaced trypsin from the trypsin-inhibitor complex. Kinetic data suggest that this displacement was a time-dependent equilibrium reaction controlled by the relative concentration of the reacting species.
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000503:physiopathology*; D002364:Caseins; D002919:Chymotrypsinogen / Q000378:metabolism*; D003094:Collagen; D004220:Disulfides; D005452:Fluoresceins; D007700:Kinetics; D051379:Mice; D010447:Peptide Hydrolases / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology*; D013438:Sulfhydryl Compounds; D014357:Trypsin / Q000378:metabolism*
chemical_list: D002364:Caseins; D004220:Disulfides; D005452:Fluoresceins; D011480:Protease Inhibitors; D013438:Sulfhydryl Compounds; D003094:Collagen; D002919:Chymotrypsinogen; D010447:Peptide Hydrolases; D014357:Trypsin