SUMMARYThe enzymic properties of 46 strains of P-lactamase-producing enteric bacteria were examined. Eight distinct types of P-lactamase were detected among these strains when substrate profile, sensitivity to p-chloromercuribenzoate (pCMB) and to cloxacillin inhibition, reaction with antiserum and charge properties are used as parameters of enzyme type. The types of enzyme detected ranged from molecules with a predominantly cephalosporinase profile to those where penicillins were hydrolysed much more rapidly than cephalosporins. The majority of isolates synthesized an enzyme that was almost equally active against penicillins and cephalosporins. To date only three of the eight types of enzyme have been shown to be transferable by conjugation.

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Phenylalanine ammonia-lyase (EC 4.3.1.5) of the yeast Rhodotorula glutinis was rapidly inactivated by duodenal juice. It was susceptible to chymotrypsin and subtilisin and to a lesser extent trypsin. Initial proteolysis of the enzyme by chymotrypsin and trypsin resulted in cleavage of the monomeric subunit (75 000 Mr) into a large (65 000 Mr) and a small (10 000 Mr) peptide. The small peptide was rapidly degraded. The 65 000-Mr fragment was resistant to prolonged incubation with chymotrypsin, but was degraded by trypsin under the same conditions. Phenylalanine ammonia-lyase was cleaved into several polypeptides by subtilisin, the 65 000-Mr peptide being totally absent. The N-terminal region of the enzyme was contained in the 65 000-Mr fragment, as was the dehydroalanine moiety, the prosthetic group. Active-site-binding ligands protect the enzyme from inactivation by the three proteinases, and peptide-bond cleavage by trypsin and chymotrypsin. Several chemical modifications were performed on phenylalanine ammonia-lyase. Some decreased its antigenicity, and ethyl acetimidate decreased the rate of degradation of the 65 000-Mr peptide by trypsin. The modification did not protect the enzyme from proteolytic inactivation of the enzymic activity. These observations are discussed in terms of the structure of phenylalanine ammonia-lyase and site of action of the proteinases.