Cyclic Photophosphorylation in Vivo and its Relation to Photosynthetic CO(2)-Fixation

Abstract

Salicylaldoxime (2 x 10(-3)m and less) inhibits cyclic photophosphorylation in intact Chlorella cells severely whereas photosynthetic O(2)-evolution and (14)CO(2)-fixation is hardly affected. Cyclic photophosphorylation in vivo was measured by following anaerobic light dependent glucose uptake. A similar difference in susceptibility has been observed with carbonylcyanide-p-trifluoromethoxyphenylhydrazone. Various controls exclude the possibility that the difference in inhibition was caused by differing experimental conditions or, in the case of glucose assimilation, by an inhibition of a reaction other than photophosphorylation.There also exists a great difference in light saturation of cyclic photophosphorylation and photosynthesis. Evidence is reported that at light saturation of glucose uptake light driven cyclic phosphorylation is indeed the limiting reaction.The results are considered as evidence that cyclic photophosphorylation does not contribute ATP stoichiometrically to photosynthetic CO(2)-fixation.