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Thioredoxin-like Activity of Thylakoid Membranes

THIOREDOXIN CATALYZING THE REDUCTIVE INACTIVATION OF GLUCOSE-6-PHOSPHATE DEHYDROGENASE OCCURS IN BOTH SOLUBLE AND MEMBRANE-BOUND FORM ¹

Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680

The inactivation of pea leaf chloroplast glucose-6-phosphate dehydrogenase by dithiothreitol can be catalyzed by thioredoxin-like molecules that are present in chloroplasts. This thioredoxin activity occurs predominantly as a soluble species, but washed thylakoid membranes also exhibit some thioredoxin-like activity. The membrane-associated thioredoxin can be extracted by treatment with the detergent Triton X-100. The solubilized thioredoxin appears to have a molecular size similar to that of the soluble thioredoxin which catalyzes the same reaction. The thylakoid-bound activity constitutes only about 5% of the total chloroplast thioredoxin activity. The thioredoxin occurring in the membrane fraction cannot, however, be ascribed to the trapping of stroma since less than 0.1% of three stromal marker enzymes are found in the same thylakoid extract.

³ Present address: Biology Department, Dickinson College, Carlisle, Pa. 17013.

¹ This study was supported by National Science Foundation Grant 77-08355 and Department of Energy Contract EP 78-S-02 4961.