[The kinetics of hydrolysis of alanine peptide esters and -p-nitroanilides by thermitase, a thermostable serine protease from Thermoactinomyces vulgaris: secondary specificity, influence of temperature and solute].

The kinetic parameters Km and kcat and the resulting proteolytic coefficients kcat/Km for the hydrolysis of blocked alanine peptide esters (X(Ala)nOMe) and -p-nitroanilides (X(Ala)n-pNA) of variable length (n = 1 to 5 alanine residues) by the cationic, microbial serine protease thermitase are determined in order to delineate the number of subsites involved in catalysis. Thermitase has at least five secondary subsites (S1 to S5) being hydrophobic in S1 to S4. Arrhenius plots for both, esterase and amidase activity were biphasic with a break at 30 degrees C, followed by a downward bend. The influence of dimethylformamide, solute for many substrates, on the thermitase-catalyzed esterolysis of Z(Ala)2OMe was also investigated. In contrast to the kcat values being unaffected by 5 to 30% dimethylformamide, the Km values increased logarithmically with enhancing its concentration.