UPTAKE AND METABOLISM OF ALLANTOIN AND ALLANTOATE BY CELLS OF CHLAMYDOMONAS-REINHARDTII (CHLOROPHYCEAE)

The green alga Chlamydomonas reinhardtii can use the ureides allantoin and allantoate as sole nitrogen sources. Once the uptake systems for allantoin and allantoate were induced, the uptake and growth rates wer e identical for the two ureides. However, the enzymatic activities inv olved in the degradation of the two ureides (allantoinase and allantoi case) were regulated differently. Allantoinase seems to be constitutiv e, since it was detected in all the nitrogen sources studied, while al lantoicase behaved as an inducible enzyme, since it was present only i n cells cultured in ureides or any metabolic precursor of these compou nds. Neither allantoinase nor allantoicase activities were repressed b y ammonium in the presence of ureides. Allantoicase activity was not i nduced under nitrogen starvation conditions, while it was induced in c ells that had been cultured with allantoin or allantoate in the dark. Allantoin uptake showed a pattern similar to that of allantoate under all nutritional and environmental conditions tested. Inhibition of all antoin and allantoate uptake by N-ethylmaleimide suggests that thiol ( SH-) groups are involved in both uptake systems. The use of both allan toin and allantoate was similarly inhibited by the metabolic poisons t ested (cyanide, azide, 2,4-dinitrophenol and 3'-(3,4-dichlorophenyl)-1 ',1'-dimethyl urea) but only at very high concentrations. The possibil ity that uptake of allantoin and allantoate might take place through t wo independent systems is discussed.