UTILIZATION OF ADENINE AND GUANINE AS NITROGEN-SOURCES BY CHLAMYDOMONAS-REINHARDTII CELLS

In Chlamydomonas reinhardtii Dangeard, adenine or guanine can be used as the sole nitrogen source for growth by means of an inducible system which is repressed by ammonia, Cells grown on either adenine or guani ne were able to take up both purines, although the adenine uptake rate was always about 40% of the guanine uptake rate, Both adenine and gua nine were taken up by an inducible system(s) exhibiting hyperbolic kin etics with identical apparent K-t values of 3.3 mmol m(-3) for adenine and 3.2 mmol m(-3) for guanine, Adenine and guanine utilization depen ded on pH, with similar optimal pH values of 7.3 and 7.4, respectively , Adenine and guanine each acted as a competitive inhibitor of the oth er's uptake, and their utilization was also inhibited by hypoxanthine, xanthine and urate, Inhibition of adenine uptake by guanine and hypox anthine was competitive, with K-i values of 5.5 and 1.6 mmol m(-3), re spectively. Guanine uptake was also inhibited competitively by adenine (K-i=1.3 mmol m(-3)) and hypoxanthine (K-i=3.3 mmol m(-3)). Utilizati on of both adenine and guanine was inhibited by cyanide, azide, 3(3,4- dichlorophenyl)-1,1-dimethyl urea, 2,4-dinitrophenol and carbonylcyani de m-chlorophenylhydrazone, and was also sensitive to p-hydroxymercuri benzoate and N-ethylmaleimide, On the basis of these results, taken to gether, the possibility that adenine and guanine are translocated into Chlamydomonas by a common system is discussed,