acid accumulation in ethionine-resistant Saccharomyces cerevisiae. J. Bacteriol. 88:20-24. 1964.-Recessive ethionine-resistant strains of Saccharomyces cerevisiae possess a genetic lesion affecting the concentration of amino acids nonspecifically in the expandable pool of the organism. This area, which may be linked to a methionine gene, is highly mutable and accounts for resistance to certain amino acid analogues. Other mutations result in ethionine resistance by a mechanism unrelated to the amino acid uptake system.

Induction of kynureninase in a homogeneous population of mycelia in balanced growth was studied. Induced synthesis of enzyme was apparent 10 min after addition of inducers (tryptophan, kynurenine, and N -formylkynurenine). Experiments with cycloheximide-inhibited cells indicated that initiation of message transcription occurred about 4 min after addition of inducers. Lifetime of the message in the absence of inducer was of the order of 5 min. Experiments with mutants showed that N -formylkynurenine was the probable inducer of physiological importance.

Induction of the methionine-activating enzyme in Saccharomyces cerevisiae. J. Bacteriol. 87:920-923. 1964.-The methionine-activating enzyme was induced in yeast in the presence of methionine, resulting in an accumulation of S-adenosylmethionine. Formation of the sulfonium derivative prevented the accumulation of high levels of free methionine in induced cells. The physiological significance of this phenomenon is discussed.

The role of cystathionine in methionine biosynthesis in wild-type and auxotrophic strains of Saccharomyces cerevisiae was studied. Homocysteine and cysteinerequiring mutants were selected for detailed study. Exogenously supplied cystathionine, although actively transported by all strains tested, could not satisfy the organic sulfur requirements of the mutants. Cell-free extracts of the wild-type, homocysteine, and cysteine auxotrophs were shown to cleave cystathionine. Pyruvic acid and homocysteine were identified as the products of this cleavage. A mutant containing an enzyme which could cleave cystathionine to homocysteine in cellfree experiments was unable to use cystathionine as a methionine precursor in the intact organisms. The significance of this finding is discussed.

SYNOPSIS. Ten‐ or 12‐day cultures of Trypanosoma ranarum in Diamond's SNB‐9 medium contain large numbers of slender crithidia and considerably smaller numbers of pear‐shaped crithidia, but in fresh media the pear‐shaped bodies constitute about 93% of the population after 5 days whereas slender forms make up about 4–5%; the remainder are leishman bodies. Succeeding days show a different cycle in that the slender forms increase to some 93% at 10–13 days and the pear bodies decrease to some 3% of the total at the same time. When washed in Krebs‐Ringer phosphate buffer alone, neither morphological type shows endogenous respiration; in glucose containing buffer, O2 consumption becomes evident; pear‐shaped crithidia use, on an average, 12.6 μl O2/hr/108 whereas slender forms utilize 17.7 μl O2/hr/108 parasites. Malonate at 0.01 m inhibits O2 consumption of slender forms about 61% as compared to 27% with the pear‐shaped bodies. A speculative discussion of the relation between morphological types, O2 consumption in the presence of glucose, and malonate inhibition is presented.