Add time:09/26/2019         Source:sciencedirect.com

Kinetic parameters for the action of bovin Factor Xa (EC 3.4.21.22) on 25 commercially available peptide p-nitroanilides have been determined. The selectivity constant, kc/Km, ranges from 1.5·101 to 2·106 M-1·s-1 for the poorest and the best substates, respectively. The best substrates for Factor Xa were identified as those with arginine in the P1 position, and glycine in the P2 position. Quantitative distinction between lysine and arginine in the P1 position and other amino acids in the P2-P4 position of the substrate is reported from the changes in the kinetic parameters for substrates differing in only a single amino acid in these positions. Effects of NaCl and CaCl2 concentrations and temperature on the action of Factor Xa on selected substrates have beeb assessed. Km values for Factor Xa hydrolysis of most substrates are greater than 100 μM. Solubility of the substrates consequently restricts measurements of reaction velocities to concentrations lower than desirable for optimally determining kc. Comparison of these kinetic parameters for Factor Xa with those of thrombin (Lottenberg R.; Hall, J.A.; Blinder, M., Binder, E. and Jackson, C.M. (1983) Biochim. Biophys. Acta 742, 539-557) for these same substrates indicates that the greater hydrotic efficiency of thrombin is due primarily to lower Km values.

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