Subcellular Localization of Sorbitol-6-phosphate Dehydrogenase in Protoplast from Apple Cotyledons

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The subcellular localization of sorbitol-6-phosphate (S6P) dehydrogenase in protoplasts of apple cotyledons was examined by differential centrifugation and linear sucrose density gradient centrifugation (30-60%, w/w) . The distribution of S6P dehydrogenase activity was 55% in the 500×g pellet of the homogenate and 35% in the supernatant of 105,000×g. When the 500×g pellet was recentrifuged in a linear sucrose density gradient, one major peak of activity was found at a density of 1.23. This peak coincided with the major peak of chlorophyll and NADP^+-triose-P dehydrogenase activity. When the 500×g pellet was sonicated, the major peak of S6P dehydrogenase activity shifted to a lighter density (d=1.18). The shifted peak also coincided with the peak of chlorophyll. The enzyme detected in the major peak of chlorophyll (d=1.23) was partially solubilized by sonic or detergent treatment, but not by hypotonic solution. The results supported the localization of S6P dehydrogenase in chloroplasts, and presumably their association with thylakoid membranes. Part of the enzyme was assumed to be naturally present in the cytosol, too.
日本植物生理学会の論文