THE METABOLISM OF GUANINE BY THE DIATOM PHAEODACYLUM TRICONUTUM BOHLIN1

Guanine taken up by intact cells of Phaeodactylum tricornutum Bohlin was rapidly converted to allantoin which accumulated in the cells; the earleir view that the compound which accumulated was a methylahypoxanthine is shown to be erroneous. In contrast, cells of P. tricornutum, after premeabilisation with toluene, converted guanine only to xanthine, the reaction presumably being catalysed by guanine diaminase. Freshly harvested N-replete cells contained substantial guanine deaminase activity (ca. 200 nmol (108 cells h)−1); this activity doubled during 5 hours of N-deprivation. During the same period, the ability to take up guanine, which was initially low, increased by about 25x.