WILD-TYPE VARIANTS OF EXOPENICILLINASE FROM STAPHYLOCOCCUS AUREUS

Abstract

Three variants of staphylococcal exopenicillinase (types A, B and C) can be distinguished on chemical, enzymological and immunological grounds. Enzyme type A has a higher specific activity than that of type B, but has a similar combination affinity with anti-(exopenicillinase type-A) serum. Enzyme types-A and-C have a similar specific activity, but enzyme type-C has a lower combination affinity for anti-(exopenicillinase type-A) serum than has enzyme type-A. The sedimentation coefficients and amino-acid analyses of the three enzyme types are similar. All three enzyme types have small but significant differences in kinetics of action when hydrolyzing benzylpenicillin, methicillin, cloxacillin and cephalosporin-C. Peptide maps, obtained from enzyme types A and C after digestion with trypsin, show that these two variants probably differ in the nature of only a very few amino-acid residues. Enzyme type-B seems to be confined to staphylococci that are members of staphylococcal phage group II. Enzyme types-A and -C are produced by staphylococci that are -nembers either of phage group I or HL but never group n. The low specific enzyme activity and affinity of enzyme type-B towards all penicillins tested suggest that this enzyme type has a lower efficiency in hydrolyzing penicillin and therefore in protecting bacteria from the action of penicillin. This could account for the low incidence among "hospital staphylococci" of penicillin-resistant staphylococci that are members of phage group EL.