MULTIENZYME SYNTHESIS AND STRUCTURE OF FACTOR-S3

Factor S3, an unusual metabolite of Propionibacterium shermanii, is bi osynthesized from porphobilinogen (PBG) by three enzymes, PBG deaminas e, uro'gen III methyltransferase (M1), and the Salmonella typhimurium cbiF gene product, isolated from recombinant strains of Escherichia co li. PBG deaminase affords uro'gen I, and M1 performs the methylation o f three beta-pyrrolic carbons of uro'gen I to form 2,7,12-trimethylpyr rocorphin I. The cbiF gene product then methylates one alpha-pyrrolic carbon (C-16). Nonenzymatic insertion of zinc into the macrocycle form s the tetramethylated zinc corphinoid factor S3.