SYNTHESIS OF TYEROSINE AND PHENYLALANINE BY LACTOBACILLUS ARABINOSUS1'2

Studies with microorganisms in a number of laboratories have contributed information con-cerning the chemical pathways which lead to the biological synthesis of phenylalanine and tyro-sine. Lyman et al. (1947) showed that Lacto-bacillus arabinosm strain 17-5 could synthesize these compounds if the basal medium was supple-mented with pyridoxine and if 6 per cent carbon dioxide was supplied as a gas phase over the liquid culture. In the absence of carbon dioxide, rapid growth took place when phenylalanine and tyrosine were present, but the removal of either of these amino acids blocked growth almost com-pletely. These experiments showed that phenyl-alanine is not converted to tyrosine by L. arabino-sus as it is in animal tissues. They also suggest the posibility that C02 may be directly utilized in aromatic amino acid synthesis by this organ-ism. Gilvarg and Bloch (1950, 1951a,b, 1952) grew Saccharomyces cerevae on a medium containing C14-glucose and showed that both tyrosine and phenylalanine are formed rather directly from glucose. Davis (1951) found mutants of Escherichia coli with a multiple requirement for tyrosine, tryptophan, phenylalanine, p-aminobenzoic acid, and p-hydroxybenzoic acid. Of particular signifi-cance was the finding that shikimic acid would substitute for this quintuple requirement ap-parently functioning as an early intermediate in aromatic synthesis. Recently, prephenic acid, an intermediate in phenylalanine synthesis in E. coli, has been isolated by Weiss et al. (1954) an