STUDIES ON THE BIOCHEMISTRY OF TETRAHYMENA. IV. AMINO ACIDS AND THEIR RELATION TO THE BIOSYNTHESIS OF THIAMINE

Abstract

1. In Eastman gelatin hydrolysate (EGH) and Factors I, II, and III from Liver Fraction L (heat- and alkali-treated to destroy thiamine) the ciliate Tetrahymena geleii W grows very poorly without added thiamine. 2. A mixture of amino acids (11 AA) with the dethiaminized liver fraction supports fair growth without added thiamine. 3. There appear to be substances in the liver fraction or the gelatin hydrolysate or both which specifically block the mechanism for the biosynthesis of thiamine. 4. This block can be released by Factor S from alfalfa extract or by the unnatural isomers of a number of amino acids. 5. Some release of the inhibition to thiamine synthesis is produced by a few of the natural amino acids but this is probably due to the presence of low concentrations of unnatural isomers which result from racemization during preparation. 6. The unnatural isomer of isoleucine (the only unnatural isomer available for testing) was found to be active in approximately one half the concentration of the dl-isoleucine. 7. Thiamine is extremely stimulatory in low concentrations. 8. The thiazole and pyrimidine components are slightly stimulatory but this stimulation appears to be due to their ability to cause some release of the thiamine synthesis inhibition.