Polyphosphate formation in Chlorella in relation to photosynthesis

Suspensions of Chlorella converted orthophosphate into cellular phosphate in the light, especially in the absence of C0 ₂ , when orthophosphate was largely transformed into polyphosphate. Polyphosphate formation continued for several hours, slowly decreasing, and was saturated at much lower light intensities than photosynthesis with 5 % C0 ₂ . It was maximum at about pH 4, decreasing to zero at pH 7-8. It was not affected by anaerobic conditions and nitrate, but decreased with glucose.

Phenylurethane inhibited polyphosphate formation less than photosynthesis, and in the light-limiting range only. Light saturation was reached at higher intensities.

DNP inhibited photosynthesis and polyphosphate formation to the same extent at all light intensities, and most strongly at low intensities. Sodium azide and NaF inhibited both processes about equally.

Probably high-energy phosphate was formed in light, and transferred to polyphosphate when photosynthesis was curtailed by lack of C0 ₂ . Glucose may also compete for this high-energy phosphate.

With C0 ₂ phosphate fixation yielded more stable products, and showed different sensitivity to inhibitors.

Dark fixation required oxygen and was especially sensitive to DNP but less so to glucose and other inhibitors.

Slow decomposition of polyphosphate and release of orthophosphate occurred in darkness under nitrogen.