Crystallization of Purines in the Vacuole of Candida utilis

Abstract

WE have reported previously that Candida utilis removes seven purines (adenine, guanine, hypoxanthine, xanthine, uric acid, 2,6-diaminopurine and isoguanine) from the medium by an active transport process when these compounds are used as sources of nitrogen for the yeast^1,2. These compounds and their metabolic products are held within the cell in high concentrations that appear to exceed the solubilities of the compounds in the volume of water available. For example, 5 gm. (wet weight) of yeast that had taken up 450 mgm. of uric acid was dried to constant weight, samples of the dried yeast were heated repeatedly in buffer at 100° C. to extract the uric acid, and the extracts were analysed with purified uricase by the method of Kalckar³. It was found that the dried yeast contained 16 per cent uric acid by weight and that 35 per cent of the uric acid administered was recovered in the extracts. It is presumed that the remaining 65 per cent of the uric acid had been metabolized via the yeast uricase. The wet yeast contained 82 per cent water, so that the concentration of uric acid would be about 35 mgm./ml. of water in the wet yeast. The solubility of uric acid is given as 2.53 mgm./100 ml. at 20° C. (ref. 4) and therefore the presence of crystalline uric acid in the yeast cell would be expected with the high concentrations that were observed.