R-factor-mediated beta-lactamases that hydrolyze oxacillin: evidence for two distinct groups.

The enzymatic and molecular properties of 14 oxacillin-hydrolyzing beta-lactamases, all of them R-factor-specified, were studied, and two distinct groups were found. Four of the enzymes had a molecular weight of 24,000, were active against methicillin, and had an electrophoretic mobility of -0.1 cm/h. Eight enzymes had a molecular weight of 45,000, low activity against methicillin, and an electrophoretic mobility of +0.5 cm/h. The remaining two enzymes were similar to those of the second group in being relatively inactive against methicillin, but their molecular weight was lower (42,000) and their electrophoretic mobility was different (-0.1 cm/h). All the enzymes of both groups were sensitive to inhibition by sodium chloride. The two groups were not completely homogeneous in their enzymatic properties; seven possible subtypes could be recognized.