REVERSIBLE THIOL-DISULFIDE EXCHANGE OF TRYPSIN AND CHYMOTRYPSINOGEN WITH A TUMOUR-DERIVED INHIBITOR - KINETIC DATA OBTAINED WITH FLUORESCEIN-LABELLED POLYMERIC COLLAGEN FIBRILS AND CASEIN AS SUBSTRATES

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 trasylol-trypsin, 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. © 1979.