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

Abstract

A number of detergents have been used to convert chloroplasts into smaller complexes for more intensive study of the properties of the photosynthetic apparatus (16). In an early series of experiments, Smith treated chloroplasts with digitonin, bile salts, sodium deoxycholate and sodium dodecyl sulfate (2325). The first 3 detergents removed and solubilized the chlorophyll while the latter split the chloroplasts into protein units containing the pigment. Other investigators have employed Zephiran chloride, Tween 20 and saponin (10), Duponol C and span 80 (4). and several anionic and cationic detergents (15). Digitonin treatment of chloroplasts has been used to release a photooxidative activity (5, 9, 13, 20) and to produce separable chloroplast fractions which contain altered chlorophyll ratios and appear to represent a separation of pigment system I (1, 3, 31). Triton X-100 effectively ruptures intact chloroplasts, and at low concentrations disrupts the sequential electron flow required for the Hill reaction (6, 10, 22). Sauer anid Park reported that in contrast to other detergenits tested, Triton X-100 causes a change in the fluorescence properties of the chloroplast at concentrations below those required to inhibit the Hill reaction (22), indicating a facile interaction of this detergent with the chlorophyll of the chloroplast. The experinments of Vernon et al. showed that chloroplasts solubilized by Triton X-100 catalyze photochemical redox reactions similar to those catalyzed by purified chlorophyll a solubilized by the same detergent (28, 30). Furthermore, Kahn isolated a chlorophyll-protein complex from chloroplasts by treatments with Triton X-100 (7). In contrast to the solubilizing effect of Triton X100 at high concentrations, lower amounts produce rather specific effects upon the intermediate electron transport complex of chloroplasts, inhibiting photophosphorylation and the related pH shift while stimulating electron flow (6, 18. 19). Because of its many effects upon the photosynthetic apparatus, an investigation into the action of this detergent upon a variety of photochemical reactions of spinach chloroplasts has been conducted and serves as the basis for this paper. Methods