Cellular Distribution of β‐Lactamase RP4 Is Mediated by an Outer Membrane Protease

RP4 β‐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. β‐Lactamase isolated from outer membrane of strains which are lacking a protease that is involved in the cleavage of colicins differs from the β‐lactamase of parental cells in substrate profile, apparent molecular weight and the ability to interconvert. The cellular distribution of β‐lactamase also differs between wild‐type and protease‐deficient mutants. Both strains have equivalent amounts of β‐lactamase in their outer membranes, however the parental strain also has considerable β‐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 β‐lactamase. This conclusion is supported by the observation that the β‐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.