Roush and Domnas ('56) found that uric acid was accumulated by an active transport process in the yeast Candida utilis (formerly known as Torulopsis utilis). Roush, Questiaux, and Domnas ('59) demonstrated similar accumulation of six other purines by the same species. The amounts of purine accumulated are so great that the purines crystallize within the vacuoles of the yeast cells (Roush, '61). Yeast harvested from a growth medium containing 5% glucose as carbon source and 0.4% ammonium sulfate as nitrogen source began to accumulate purines only after a "lag" of some 30-90 minutes in media containing 5% glucose and no nitrogen source except the purines. Preincubation in media containing glucose but no purine eliminated this lag, permitting immediate uptake of purines added at the end of the incubation period. In order for such pretreatment to be effective, it was necessary that glucose be present, and ammonium sulfate absent (or present at only very low concentrations); oxygen was not required during the pre-incubation period, nor during the subsequent uptake.
Roush et al. ('59) suggested that the lag or pre-adaptation period before purine uptake might reflect the need to accumulate an energy source or to form a specific binding site, or both. The experiments reported here support the hypothesis that accumulation of an energy source is a major function of the lag period.
Methods
Candida utilis (strain ATCC 9950) was grown in the basal medium of Schultz and Atkin ('47) supplemented with 5% glucose and 0.4% ammonium sulfate, at 25"-30"C, with constant aeration, and harvested by centrifugation at 5Β°C. After