Über die Beziehungen zwischen Phosphathaushalt und Photosynthese III

Abstract

The effect of various enzyme poisons on glucose assimilation by Chlorella in light and in darkness was studied. Only arsenate and o-phenanthroline caused an inhibition to the same extent under both conditions, whereas monoiodoacetic acid, fluoride, fluoro-acetic acid malonate, 2-4-dinitrophenol, azide, arsenite, and cyanide caused considerably less inhibition in light than in darkness. A correlation between the degree of inhibition of glucose assimilation and photosynthetic O2 production was not apparent. In accordance with observations previously reported the increased glucose assimilation was considered as an indicator of a light-dependent phosphorylation. The equal inhibition of glucose assimilation in light and in darkness by arsenate supports this idea. The possibility of the formation of energy-rich phosphate by the increased oxidative degradation of intermediate products of photosynthesis can not be drawn upon as an explanation of the assimilation of glucose in light, since all poisons that block the substrate way (monoiodoacetic acid, fluoride, fluoroacetic acid, arsenite, malonate) increase the light-darkness difference. Likewise, the formation of energy-rich phosphate by way of respiratory chain phosphorylation on the basis of recombination of the hydrogen with O2 produced by photosynthesis can not be the basic mechanism of light-dependent phosphorylation since all uncoupling poisons (2-4-dinitrophenol, azide), just as the blocking of the cytochrome system by cyanide, cause less inhibition of glucose uptake in light. It is, however, entirely possible that under normal conditions the formation of energy- rich phosphate in this way goes on along with the real "light phosphorylation." Since only the blocking of the primary photosynthetic process by o-phenanthroline causes an equal inhibition of glucose assimilation in light and in darkness it is assumed that phosphorylation is directly involved in the primary reaction of photosynthesis or that the adenylic acid system is in equilibrium with a compound of high group potential formed in connection with light absorption.