Partial characterization of phosphoribosyl transferase, phosphoribosyl anthranilate isomerase, and indole glycerol phosphate synthase from Serratia marcescens.

The molecular organization of the enzymes phosphoribosyl (PR) transferase, phosphoribosyl anthranilate (PRA) isomerase, and indole glycerol phosphate (InGP) synthase of the tryptophan biosynthetic pathway of Serratia marcescens was investigated and compared with that reported in other enteric bacteria. PRA isomerase and InGP synthase activities were found to reside in a single polypeptide chain, a situation analogous to that in Escherichia coli, Salmonella typhimurium, and Aerobacter aerogenes. This bifunctional enzyme was purified to near homogeneity. Its molecular weight was estimated to be 48,000. PR transferase was found unassociated with PRA isomerase and InGP synthase after gel filtration and ion-exchange chromatography. Whereas in other enteric organisms PR transferase has been reported to form an aggregate with anthranilate synthase, it is a distinct entity in S. marcescens.