REGULATION OF CHEMOAUTOTROPHIC METABOLISM .2. COMPETITION BETWEEN AMINO ACIDS FOR INCORPORATION INTO THIOBACILLUS

Incorporation of 14C-phenylalanine by T. neapolitanus was inhibited competitively by relatively low concentrations of glycine, serine, alanine, valine, leucine, isoleucine, tryptophan, tyrosine, histidine, threonine, and methionine (Group I amino acids), but not greatly depressed by aspartate, glutamate, lysine, arginine, cysteine (Group II amino acids) and proline at similar concentrations. Group I acids competed with each other for incorporation but were little affected by Group II acids. Similarly Group I acids little depressed the incorporation of Group II acids, among which, however, some mutual inhibition occurred. Incorporation of proline was depressed by both Group I and II acids. Two main permeation mechanisms are proposed, one transporting Group I acids, the other Group II acids, but some overlapping of function probably occurs. Proline may be transported by a third permease, which is subject to inhibition by both Group I and II acids. T. concretivorus also has a common transport mechanism for some amino acids. Less interaction between amino acids was found using two heterotrophic pseudomonads. Exogenous phenylalanine inhibited both the biosynthesis and the uptake of tyrosine and tryptophan by T. neapolitanus. High phenylalanine concentrations depressed the assimilation of 14C-labelled tyrosine and tryptophan less than low ones, suggesting that the bacteria developed a requirement for external tyrosine and tryptophan when exposed to highly inhibitory concentrations of phenylalanine. © 1969 Springer-Verlag.