Glucose‐6‐phosphate Utilization by Marine Algae¹

SUMMARY A good relationship was found between the amount of phosphatase present at the surface of marine unicellular algae and their ability to utilize glucose‐6‐phosphate (G‐6‐P) as a phosphorus source. Algae did not take up the whole molecule of G‐6‐P; those with phosphatase hydrolyzed the ester extracellularly and assimilated the PO 4 . The phosphatases were usually phosphate‐repressible, and they usually showed optimum activity at pH ± 7. Algae lacking phosphatases that could act on external substrates did not assimilate G‐6‐P; they became phosphorus‐deficient and stopped growing. Of 13 species studied, only Cyclo‐tella cryptica was capable of assimilating glucose for cell growth in darkness. Cyclotella utilized both the glucose and the phosphate of G‐6‐P, but only after hydrolysis by the alkaline phosphatase at the cell surface.