Photosynthetic phosphorylation in the presence of vitamin B 6

Abstract

Two forms of vitamin B 6, pyridoxal-5-phosphate and pyridoxal hydrochloride, support photosynthetic phosphorylation with spinach chloroplast fragments while other forms of vitamin B 6, including 4-pyridoxic acid, pyridoxamine dihydrochloride, pyridoxamine phosphate monohydrate, pyridoxine hydrochloride, and deoxypyridoxine-5-phosphate, were not active. Photosynthetic phosphorylation supported by pyridoxal phosphate occurs at a rate of 168 μmoles of adenosine triphosphate formed per mg. chlorophyll per hour. The pyridoxal phosphate supported reaction was linear with time and chlorophyll concentration, was not greatly affected by anaerobic conditions, gave a sigmoid response with increasing light intensity and was sensitive to the action of uncouplers and inhibitors. The presence of pyridoxal phosphate inhibited photosynthetic phosphorylation supported by methyl phenazonium methosulfate and ferricyanide without affecting that supported by nicotinamide adenine dinucleotide phosphate plus photosynthetic pyridine nucleotide reductase.