PHOTOCHEMICAL ACTIVITIES OF SONICATED LAMELLAE OF SPINACH CHLOROPLASTS WITH SPECIAL REFERENCE TO THE ACTION OF CRS (CYTOCHROME C REDUCING SUBSTANCE)

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Abstract
The photooxidation of reduced DPIP with NADP and O2 as final electron acceptors was studied with sonicated lamellae of spinach chloroplasts, with special reference to the possible role of CRS, a newly discovered factor of photochemical system I. A correlation between inactivation of NADP-photoreduction and dissolution of CRS was observed on treatment of the lamellae with various organic solvents. The treatment also suppressed the O2-linked photooxidation of reduced DPIP, although the suppression was not so marked as in the former reaction. The suppressed photooxidation of reduced DPIP (with O2 and NADP as electron acceptors) was partially restored on addition of dyes of negative redox potential, such as methyl viologen. The experimental results indicate that a factor participates in the reactions of photochemical system I, probably functioning as an electron carrier coupling the photooxidation of P700 with the reduction of ferredoxin or O2. The finding that the above mentioned activity of the factor is destroyed by treatments which are effective in solubilizing CRS from the chloroplasts suggests the identity of the factor with CRS.