Cellular distribution of beta-lactamase RP4 is mediated by an outer membrane protease

RP4 beta-lactamase extracted from the outer membrane of wild-type Escherichia coli can be resolved into several interconvertible forms that differ in their stabilities, substrate profiles and apparent molecular weights. beta-Lactamase isolated from outer membrane of strains which are lacking a protease that is involved in the cleavage of colicins differs from the beta-lactamase of parental cells in substrate profile, apparent molecular weight and the ability to interconvert. The cellular distribution of beta-lactamase also differs between wild-type and protease-deficient mutants. Both strains have equivalent amounts of beta-lactamase in their outer membranes, however the parental strain also has considerable beta-lactamase in the cytoplasmic membrane while the mutant does not. In addition the mutant contains only 30% of the parental level of enzyme in the periplasm. It is proposed that the reduced level of periplasmic enzyme is the result of a defect in processing of membrane-associated beta-lactamase. This conclusion is supported by the observation that the beta-lactamase isolated from the mutant can be converted to forms resembling those found in the parent by incubation with extracts or outer membrane isolated from the parent.