Biosynthesis of chloramphenicol in Streptomyces sp. 3022a. Properties of an aminotransferase accepting p-aminophenylalanine as a substrate.
In the presence of alpha-ketoglutarate, cell-free extracts of Streptomyces species 3022a catalysed transfer of the amino group from p-aminophenylalanine, yielding an unstable product similar to that obtained by the action of D- and L-amino acid oxidases on the amino acid. The enzyme, purified 16-fold from cell homogenates by chromatography on ion-exchange celluloses, hydroxyapatite, and cross-linked dextran gel, has a molecular weight of 90 000 and a broad pH optimum at 8.0. It is active with L-phenylalanine and L-tyrosine as well as p-amino-DL-phenylalanine as amino donors, and its relative activity towards these substrates did not change during purification. Polyacrylamide disc-gel electrophoresis of the partially purified enzyme gave single zones with identical mobility when the gels were assayed for activity with p-aminophenylalanine and tyrosine as amino donors. The results indicate that synthesis of p-aminophenylalanine en route to chloramphenicol uses a multispecific aminotransferase for aromatic amino acids. With L-phenylalanine as substrate, the preferred amino-accepting co-substrate was alpha-ketoglutarate. Some kinetic constants for the enzyme were determined, and its requirement for pyridoxal phosphate was demonstrated.
D000599:Amino Acids, Diamino / Q000378:metabolism; D002474:Cell-Free System; D002701:Chloramphenicol / Q000096:biosynthesis*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity; D000637:Transaminases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D000599:Amino Acids, Diamino; C009722:4-aminophenylalanine; D014443:Tyrosine; D010649:Phenylalanine; D002701:Chloramphenicol; D000637:Transaminases