| pubmed-article:6448639 | pubmed:abstractText | The steady-state kinetic parameters of the tripeptides D-Val-Leu-Lys-, Ala-Phe-Lys-, and < Glu-Phe-Lys- in which the free carboxyl group was substituted with p-nitroaniline (substrate) or chloromethane (inhibitor), towards the serine proteinases plasmin (EC 3.4.21.7), thrombin (EC 3.4.21.5), urokinase, factor Xa, and trypsin (EC 3.4.21.4) were investigated. The p-nitroanilide derives were found to be very good substrates for plasmin, 2.5--40-times less efficient towards trypsin and very poor (100--10 000-times less efficient) substrates for thrombin, factor Xa and urokinase. The chloromethyl ketone derivatives were comparably efficient inhibitors of plasmin and trypsin and in general very poor (100--10 000-times weaker) inhibitors of thrombin, factor Xa and urokinase. D-Val-Leu-Lys-pNA however was a very poor substrate but D-Val-Leu-Lys-CH2Cl a very efficient inhibitor for thrombin. The variability in susceptibility of the substrates towards the enzymes was due to differences in their Michaelis constant, in their deacylation rate constant or both. the variable efficiency of the inhibitors was mostly due to differences in their dissociation constant and much less to differences in their alkylation rate constant. Only a poor correlation (r = 0.25) was found between the efficiency of the p-nitroanilides as substrate and their homologous chloromethyl ketones as inhibitor. The most notable discrepancy was observed with the D-Val-Leu-Lys derivatives towards thrombin. | lld:pubmed |
