Allantoin transport in Saccharomyces cerevisiae

Allantoin uptake in both growing and resting cultures of Saccharomyces cerevisiae occurs by a low-Km (ca. 15 micrometer) transport system that uses energy that is likely generated in the cytoplasm. This conclusion was based on the observation that transport did not occur in the absence of glucose or the presence of dinitrophenol, carbonyl cyanide-m-chloro-phenyl hydrazine, fluoride, or arsenate ions. Normal uptake was observed, however, in the presence of cyanide. The rate of accumulation was maximal at pH 5.2. In contrast to the urea transport system, allantoin uptake appeared to be unidirectional. Preloaded, radioactive allantoin was not lost from cells suspended in allantoin-free buffer and did not exchange with exogenously added, nonradioactive allantoin. Treatment of preloaded cells with nystatin, however, released the accumulated radioactivity. Allantoin accumulated within cells was isolated and shown to be chemically unaltered.