Hydrolysis of plasma kallikrein by trypsin and plasmin and the formation of active fragments.

Active plasma kallikrein (Mr = 90,000) can be separated by reduction of the disulfide bridges into a heavy-chain (Mr = 45,000) and a light-chain (Mr = 36,000). A partially active fragment, corresponding to the light-chain, was isolated during the purification of active human plasma kallikrein. Bovine trypsin can form a fragment corresponding to the heavy-chain when incubated with plasma kallikrein; plasmin also causes the formation of the heavy-chain but at a slower rate. High molecular weight kininogen decreases the rate of cleavage of kallikrein by both enzymes. Light-chain does not accumulate during incubation with these proteases and the heavy-chain, after prolonged incubation is also digested. Incubation of labelled active kallikrein with plasma causes formation of fragments corresponding to the heavy- and the light-chain.