NEW-TYPE OF HEXAMERIC ORNITHINE CARBAMOYLTRANSFERASE WITH ARGINASE ACTIVITY IN THE CEPHAMYCIN PRODUCERS STREPTOMYCES-CLAVULIGERUS AND NOCARDIA LACTAMDURANS

The ornithine carbamoyltransferases (OTCases) from the beta-lactam-pro ducing actinomycetes Streptomyces clavuligerus and Nocardia lactamdura ns have been purified to near-homogeneity by delta-N-phosphonoacetylor nithine-Sepharose 4B affinity chromatography. The S. clavuligerus and N. lactamdurans OTCase monomers had a molecular mass of 37 kDa. The na tive OTCases of S. clavuligerus, N. lactamdurans and Streptomyces coel icolor had molecular masses of 248, 251 and 247 kDa respectively, whic h correspond to a hexameric structure. The apparent K-m values for orn ithine and carbamoylphosphate of the S. clavuligerus enzyme were respe ctively 2.3 and 6.0 mM at pH 8.0. The enzyme showed a reverse activity on citrulline and used lysine and putrescine as substrates. The hexam eric complex showed coupled arginase-OTCase activities and was able to convert arginine into citrulline in a carbamoylphosphate-dependent ma nner. The requirement for carbamoylphosphate might prevent the arginas e-OTCase complex from carrying out a futile cycle of arginine biosynth esis and degradation.