Sulfolipid Metabolism in Chlorella

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Abstract
Sul-foquinovosyl glycerol is a major S compound in Chlorella ellipsoidea. When the alga was incubated in radiosulfate for 1 hour, equal amounts of radioactivity were found in sulfolipid and glutathione, but none was detected in sulfoquinovosyl glycerol. No assimilation of sulfate was observed under anaerobic darkness. To elucidate the function of sulfolipid in algal cells, uniformly S35-labeled Chlorella cells, were transferred to S-deficient culture medium or nonlabeled normal culture medium and the changes of radioactivity in sulfolipid and the related compounds were followed. On incubating S35-labeled algal cells in S-deficient medium under photosynthetic conditions, the amounts of radioactivity in sulfate, sulfoquinovosvl, sulfoquinovosyl glycerol and sulfolipid decreased rapidly. When S35-labeled cells were cultured photo-autotrophically in unlabeled medium, no decrease of radioactivity was observed in sulfoquinovosyl glvcerol and sulfolipid. A decrease of S35 sulfolipid and an increase of S35-sulfolipid and an increase of S35-sul-foquinovosyl glycerol were observed when the uniformly labeled algal cells were illuminated in CO2-free air. When S-deficient Chlorella cells were incubated with S35-sulfolipid under photosynthetic conditions, significant radioactivity was found in the insoluble fraction of the cells. The same effect was also observed when normal Chlorella cells were incubated with C14-sulfolipid and CO2-free air. It is inferred from these observations that sulfolipid is an important reservoir of reduced sulfate and C compounds. In order to ascertain if the sulfolipid is involved in the mechanism of photosynthetic oxygen evolution, the rateof photosynthesis was measured during the incubation of S35-labeled cells in a S-deficient medium. Parallelism was not observed between the rate of photosynthetic activity and the decrease of sulfolipid.