Photoassimilation of Glycolate, Glycine and Serine by Euglena gracilis

SYNOPSIS. Glycolate was readily utilized for growth by Euglena gracilis , strain Z, in the light at pH 3.8 under a variety of atmospheric conditions, including CO₂-free air and nitrogen. Glycolate did not support growth in the dark as sole carbon source; no significant uptake of glycolate was observed under these conditions. However, cells grown in the light with glycolate as sole carbon source were still capable of glycolate uptake for up to 3 hr after transfer to darkness, and glycolate was taken up by cells utilizing glucose in the dark. The energy requirement for glycolate utilization could thus be met either by light, or by the aerobic metabolism of glucose in the dark. DCMU, an inhibitor of photosystem II, inhibited photoassimilation of glycolate. In the light, but again not in the dark, glycine and serine also served as sole source of carbon under CO₂-free air, but not under nitrogen. Net release of ammonia to the medium accompanied the photoassimilation of glycine and serine. Of the several metabolicallyrelated compounds tested, only glycolate was utilized as sole carbon source in the light under "anaerobic" conditions. A lag in net chlorophyll synthesis occurred during the photoassimilation of glycolate glycine or serine. Determination of rates of photosynthetic ¹⁴CO₂ fixation confirmed that some inhibition of photosynthetic capacity had occurred in response to utilization of glycolate and related compounds.