Hydrolyzes penicillin, ampicillin and carbenicillin but not other antibiotics including oxacillin, methicillin and cloxacillin. a beta-lactam + H2O = a substituted beta-amino acid Inhibited by p-chloromercuribenzoate but not by cloxacillin. Monomer. Constitutive (at protein level). Belongs to the class-A beta-lactamase family. Extended N-terminus.