title: The non-Michaelian action of thrombin on peptide p-nitroanilide substrates.
abstract: 1. v([S]) kinetic data were obtained for the hydrolysis of the chromogenic substrates H-D-Phe-L-Pip-L-Arg-pNA (S-2238), H-D-Ile-L-Pro-L-Arg-pNA (S-2288), Tos-Gly-L-Pro-L-Arg-pNA (Tos-Ch-TH) and Cbz-Gly-L-Pro-L-Arg-pNA (Cbz-Ch-TH) by native human thrombin under different experimental conditions (Pip is pipecolyl, pNA is p-nitroanilide, Tos is tosyl and Cbz is benzyloxycarbonyl). 2. The data were fitted to rational functions of order 1:1, 2:2 and 3:3 by using non-linear regression. Discrimination between equations of different degree was made using the F-test. 3. In all, 24 curves were fitted. In 17 cases degree 2:2 was significantly better than degree 1:1 at a confidence level of 95%. In no case was any further significant improvement found with functions of degree 3:3. 3. Our results allow us to assert that native human thrombin is an enzyme that does not allow Michaelian kinetic behaviour when acting on chromogenic substrates. Instead, the empirically obtained steady-state data require mechanisms whose rate equation is at least of degree 2:2.
mesh_terms: D000813:Anilides / Q000378:metabolism*; D002863:Chromogenic Compounds / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D009842:Oligopeptides / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*
chemical_list: D000813:Anilides; D002863:Chromogenic Compounds; D009842:Oligopeptides; C014413:chromozym TH; C040410:carbobenzoxyglycyl-prolyl-arginine-4-nitroanilide; D013917:Thrombin