β-lactamase

β-lac·ta·mase (lakґtə-mās) [EC 3.5.2.6] any of a group of bacterial enzymes of the hydrolase class, produced by almost all gram-negative species, that catalyze the cleavage of β-lactam rings; such rings occur in penicillins and cephalosporins so that these antibiotics are inactivated by β-lactamases. Individual enzymes are produced by different bacterial species and are called also penicillinases or cephalosporinases on the basis of their specificities. The enzymes may occur bound to membranes, extracellularly, or in the periplasmic space, may be encoded on the chromosome or on a plasmid, and may be constitutive or inducible.