KINETIC-STUDY OF PENICILLIN ACYLASE FROM ALCALIGENES-FAECALIS

Penicillin acylase from Alcaligenes faecalis has a very high affinity for both natural (benzylpenicillin, K-m = 0.0042 mM) and colorimetric (6-nitro-3-phenylacetamidobenzoic acid, K-m = 0.0045 mM) substrates as well as the product of their hydrolysis, phenylacetic acid (K-i = 0.0 16 mM). The enzyme is partially inhibited at high benzylpenicillin con centrations but the triple SES complex formed still retains 43% of the maximal catalytic activity; the affinity of benzylpenicillin for the second substrate molecule binding site is much lower (K-S' = 54 mM) th an for the first one. Phenylmethylsulfonyl fluoride was shown to be a very effective irreversible inhibitor, completely inactivating the pen icillin acylase from A. faecalis in a few minutes at micromolar concen trations; this compound was used for enzyme active site titration. The absolute values of the determined kinetic parameters for enzymatic hy drolysis of 6-nitro-3-phenylacetamidobenzoic acid (k(cat) = 95 s(-1) a nd k(cat)/K-m = 2.1 x 10(-7) M-1 s(-1)) and benzylpenicillin (k(cat) = 54 s(-1) and k(cat)/K-m = 1.3 x 10(-7) M-1 s(-1)) by penicillin acyla se from A. faecalis were shown to be highest of all the enzymes of thi s family that have so far been studied. (C) 1997 Federation of Europea n Biochemical Societies.