. Biological structure and function; proceedings. Biochemistry; Cytology. PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 361 The marked effectiveness of phenazine methosulphate could be ex- plained by its acting as an electron carrier that bypasses a rate-limiting step in photosynthetic phosphorylation [66]. This is suggested by the observa- tion of Geller [66] that the severe inhibition of photophosphorylation in R. riibrian by antimycin A does not occur in the presence of phenazine methosulphate. On this hypothesis phenazine methosulphate might give higher rates of phosphor
. Biological structure and function; proceedings. Biochemistry; Cytology. PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 361 The marked effectiveness of phenazine methosulphate could be ex- plained by its acting as an electron carrier that bypasses a rate-limiting step in photosynthetic phosphorylation [66]. This is suggested by the observa- tion of Geller [66] that the severe inhibition of photophosphorylation in R. riibrian by antimycin A does not occur in the presence of phenazine methosulphate. On this hypothesis phenazine methosulphate might give higher rates of phosphorylation at high light intensity when there is a rapid flux of electrons from excited chlorophyll. Assuming, however, several sites of phosphorylation in the cyclic pathway, the advantage of phenazine methosulphate might disappear at loic light intensity when the overall rate Low light Intensity (3000 Lux). vit. K, PMS 10 15 20 25 minutes Fig. 9. Effect of vitamin K^ and phenazine methosulphate (PMS) on anaerobic cyclic photophosphorylation in spinach chloroplasts at a limiting light intensity (3000 Lux). Reaction mixture included chloroplast fragments (C,,) containing i mg. chlorophyll and in micromoles: tris buffer, pH 8-3, 80; K2H^'-P04, 15; MgS04, 5; ADP, 15; vitamin K:, or PMS, 03; gas phase nitrogen (Tsujimoto, Hall, and Arnon [92]). of the process is limited by the electron flux. Under such conditions the highest rate of photophosphorylation would be observed in a system in which none of the phosphorylation sites was bypassed. Thus, a com- parison of photosynthetic phosphorylation, catalyzed by vitamin K and phenazine methosulphate under conditions of limiting light, seemed desirable. The results of such a comparison are shown in Y'\<g. 9. At low light intensity photophosphorylation catalyzed by vitamin Kg was markedly greater than that catalyzed by phenazine methosulphate (or pyocyanin). This diflFerence was persistent and gave a straight-line relationship for a consi
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