Some properties of a D-alanine carboxypeptidase in envelope fractions of Neisseria gonorrhoeae

Abstract

Envelope preparations of Neisseria gonorrhoeae strain GC1 (a stable, piliated strain of intermediate colony morphology) and type T1 possess a D-alanine carboxypeptidase which releases the terminal alanine residue from the uridine 5'-diphosphate-N-acetyl muramylpentapeptide substrate (isolated from Bacillus cereus T). The D-alanine carboxypeptidase of the GC1 envelopes has a broad pH optimum between pH 8.0 to 10.0. When the molarity of the tris(hydroxymethyl)aminomethane buffer was varied, the activity showed an optimum over the range 0.2 to 0.4 M. Activity was higher (135% of control level) when 20 to 80 mM Mg2+ was present. The Km for the enzyme was 0.25 mM. The D-alanine carboxypeptidase was inhibited by several beta-lactam antibiotics and the 50% inhibitory levels were 10(-8) M penicillin G, 10(-8) M ampicillin, 10(-5) M cloxacillin, and 5 x 10(-7) M methicillin.