Purification and properties of beta-lactamase from Proteus morganii

Abstract

The cephalosporin .beta.-lactamase was purified from a strain of P. morganii that showed resistance to .beta.-lactam antibiotics and produced the enzyme constitutively. The purified enzyme preparation gave a single protein band on polyacrylamide gel electrophoresis and consisted of a single polypeptide of MW 38,000-40,000 from gel filtration of Sephadex G-100 and sodium dodecyl sulfate-acrylamide gel electrophoresis, its isoelectric point being pH 7.2. No cysteine residue was found in its amino acid composition. The specific activity was 190 .mu.mol/min per mg of the purified enzyme protein for the hydrolysis of cephaloridine, the optimal pH was about 8.5, the optimal temperature was 50.degree. C. Antibodies against the purified .beta.-lactamase inhibited not only the enzyme activity of the purified preparation, but also the enzyme activity of all of the other strains of P. morganii so far tested, regardless of whether the modes of their production were inducible or constitutive. None of the .beta.-lactamases produced the .beta.-lactam antibiotic-resistant strains of other Proteus spp. was affected at all by the antibodies, thus showing that the purified cephalosporin .beta.-lactamase was of the species-specific type. The enzymological properties of the preparation were compared with those of .beta.-lactamases derived from other gram-negative enteric bacteria [Pseudomonas aeruginosa, Escherichia coli and Enterobacter cloacae].