Abstract
The specificity of proteinase K [EC 3.4.21.?] towards amino acid and oligopeptide nitroanilide substrates was investigated. The active center of the enzyme contains an extended binding region consisting of several subsites. An integral part of the S1-subsite are hydrophobic areas which were investigated by systematic elongation of the C skeleton in carboxylic acid 4-nitrophenyl esters. On the basis of these studies, a possible model of the S1-binding site is proposed. Kinetic parameters for the hydrolysis of substituted phenyl acetates catalyzed by proteinase K were measured at pH 7 and 25.degree. C. Deacylation of an acyl-enzyme intermediate is probably the rate-limiting step. Acylation (kcat/Km used as a measure) is modestly sensitive to the .sigma. values of the substituents (.rho. = 1.33, r = 0.9108), indicating electrophilic assistance by the enzyme in the catalytic mechanism. Hydrophobic forces apparently are not involved in the binding of the leaving group.