Non-competitive sulphanilamide antagonists for yeasts.

Sulphanilamide inhibition of the growth of certain yeasts and yeastlike organisms was overcome in a non-competitive manner by methionine, adenine and histidine, which are therefore regarded as end-products of enzyme systems for which p-aminobenzoic acid is essential. The methionine system was the most sensitive to sulphanilamide, followed in order by those of adenine and histidine. In the presence of methionine, adenine and histidine together, the test organisms were still sensitive to sulphanilamide, implying that p-aminobenzoic acid is concerned in still another system, or systems. The nature of these systems is obscure, but the inhibition is not overcome by purines, pyrimidines or pteroylglutamic acid, nor by single amino-acids, except in one case when m-cysteine showed some effect. In another case, a low concentration of choline chloride was effective.