| Summary: | A comparative study of the photosensitization of isolated membranes of pigmented and non-pigrmented Sarcina lutea in the presence and absence of an exogenous photosensitizer has been made. Illumination of Membranes at low light intensities with tolaidine blue resulted in photoinactivation of malate, succinate, lactate and ascorbate oxidases. Methylene blue and DCPIP reductions, cytochrome c and ascorbate-TMPD oxidase activities also showed photoinactivations. Photoinactivation was always greater in non-pigmented than in pigmented membranes. 20 minutes' illumination caused reversible inactivation, while 60 minutes' illumination caused irreversible photoinactivation of malate oxidase activity in the non-pigraented membranes. 5 minutes' illumination at high light intensity, without exogenous photosensitizer, caused reversible photoinactivation of malate and succinate oxidases and malate s DCPIP and succinate : DCPIP reductions in pigmented membranes. Non-pigmented membranes showed irreversible photoinactivation of these enzyme activities. Photoinactivation of malate : vitamin K reductase was reversible in all membranes. 15 minutes illumination irreversibly photoinactivated malate and succinate oxidases, but reversibly photoinactivated malate and succinate : DCPIP reductions in the pigmented membranes. Non-oigmented membranes showed irreversible photoinactivation of these enzyme activities. Malate and succinate : vitamin K reductases of both strains showed reversible photoinactivation. 25 minutes illumination with ultraviolet-filtered light showed no photoinactivation of PMS or methylene blue reductions, but showed reversible photoinactivation of malate oxidase activity in the pigmented strain and irreversible photoinactivation in non-pigmented cells and membranes. There was irreversible photo-inactivation of raalate : DCPIP reduction in both strains. Permanent photoinactivation of NADH oxidase activity was observed in pigmented membranes, while NADH : DCPIP reduction showed no photoinactivation. Malate : vitamin K reductase activity in both strains showed reversible photoinoxtivation. The malate oxidase and malate : vitamin K redactase activities of two other non-pignented mutants showod identical properties. It is concluded that carotenoid reduces photoinactivation generally in the presence of an exogenous photosensitizer, but protects a specific sito in the respiratory chain in the absence of added dye.
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