Photochemical Activities of Spinach Chloroplasts Following Treatment with the Detergent Triton X-100

Abstract

Spinach chloroplasts treated with various levels of Triton X-100 were examined for their ability to perform a variety of photosynthetic electron transfer reactions. In general, 3 responses were elicited by increasing concentrations of the detergent. Low levels markedly stimulated all electron transfer reactions investigated, including ferricyanide, 2,6-dichlorophenolindophenol, NADP, and cytochrome c Hill reactions. The photoreduction of NADP by ascorbate plus 2, 6-dichlorophenolindophenol also was stimulated. These stimulations showed sharp maxima at about 0.007% Triton (0.008-0.009 for NADP photoreduction). At these concentrations photophosphorvlation was almost completely uncoupled. This was the major cause of the increased rates of electron flow. However, thephotoreduction of NADP supported by ascorbate plus tetramethyl-p-phenylenediamine also was stimulated slightly in this region. Since this reaction is supposed not to support ATP formation, some additional structural modification of the chloroplast may be involved. At Triton levels of 0.01 to 0. 02% the electron transfer reactions became inhibited. There was some residual activity in the ascorbate plus 2,6-dichlorophenolindophenol-coupled reduction of NADP, however, This inhibition was most likely due to disruption of the oxygen-evolving system along with interference of the electron transfer comples. Plastocyanin is removed under these conditions. Increasing the Triton concentration about 0. 02% allowed the following reactions to reappear: cytochrome c reduction supported by reduced trimethylbenzoquinone, cytochrome c photooxidation by oxygen, NADP photoreduction supported by ascorbate plus 2, 6-dich-lorophenolindophenol, and NADP photoreduction coupled to cytochrome c oxidation. Except for the cytochrome photoreduction reaction with reduced trimethylbenzoquinone, plastocyanin either was required or markedly stimulated the reactions.