Kinetic analysis of the interaction of human tissue kallikrein with single-chain human high and low molecular weight kininogens.

Human low molecular weight kininogen (LMWK) and high molecular weight kininogen (HMWK) have been purified to apparent homogeneity as intact, single-chain molecules. When they interacted with homologous urinary kallikrein, 0.9 mol of kinin per mol of substrate was released from LMWK and 0.7 mol of kinin per mol of substrate was released from HMWK. These functionally and structurally intact substrates have been used to obtain the kinetic constants for kinin release by purified human tissue kallikreins. With human urinary kallikrein, apparent second-order rate constants (kcat/Km) of 1.46 X 105, 8.6 X 104, and 5.08 X 104 M-1.S-1 were obtained with LMWK, HMWK, and alpha-N-p-tosyl-L-arginine methyl ester (TAMe), respectively; with human pancreatic kallikrein, values of 8.7 X 103 and 7.3 X 104 M-1.S-1 were obtained with HMWK and TAMe. These values, which are comparable to those obtained for other enzyme-protein substrate interactions, indicate that LMWK is only slightly preferred to interactions, indicate that LMWK is only slightly preferred to HMWK as the natural substrate for urinary kallikrein and that HMWK as the natural substrate for urinary kallikrein and that HMWK is a somewhat better substrate for urinary kallikrein than for pancreatic kallikrein. Although the data obtained have been shown by NaDodSO4/polyacrylamide gel electrophoresis to reflect cleavage of the substrate at two points, the linear Line-weaver-Burk plots suggest that one cleavage is rate limiting. Because the plasma concentrations of both LMWK and HMWK are approximately 1/10th the Km values obtained, substrate concentration may also play a role in determining the rate at which tissue kallikreins release kinins from kininogen substrates either in the circulation or extravascularly.