The exoceliular , B - lactamase of Streptomyces albus G

The exoceilular f-lactamase of Streptomyces albus G has been purified to near protein homogeneity. It consists of one single polypeptide chain of mol.wt. 30000-31000, has a rather low isoelectric point (at pH 6.0) and contains less lysine (2.1%) and more half-cystine residues than most fi-lactamases from other Gram-positive bacteria. Penicillins are much better substrates than A3-cephalosporins; the catalytic-centre activity of good penicillin substrates is 333-500s-'. The exocellular, mol.wt. 17000 DD-carboxypeptidase of S. albus G [previously purified to protein homogeneity; Duez, Frere, Geurts, Ghuysen, Dierickx & Delcambe (1978) Biochem. J. 175, 793-8001 behaves as an exceedingly poor ff-lactamase, hydrolysing benzylpenicillin into benzylpenicilloate 5 x 10-6-fold less rapidly than does the exocellular f-lactamase. To all appearances, the f-lactamase has no bivalent cation requirement whereas, as shown elsewhere [Dideberg, Charlier, Dupont, Vermeire, Frere & Ghuysen (1980) FEBS Lett. 117, 212-214, and Dideberg, Joris, Frere, Ghuysen, Weber, Robaye, Delbrouck & Roelands (1980) FEBS Lett. 117, 215-2181, the DD-carboxypeptidase possesses one essential Zn2+ ion per molecule. Peptide 'mapping' and immunological studies suggest that the two Streptomyces enzymes probably have very different structural and mechanistic properties.