[Regulation of glucose-6-phosphate dehydrogenase in spinach chloroplasts by light].

1. The activity of the glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADPH oxidoreductase, EC 1.1.1.49) in the homogenate of illuminated leaves of Spinacea oleracea L. (30 min with 30000 Lux) is about 30% lower than in the dark controls. 2. Illumination of isolated chloroplasts (10000 Lux) causes a fast inhibition of the enzyme activity which reaches about 45% after 20 min. 3. The activity of the 6-phosphogluconate dehydrogenase (6-phospho D-gluconate: NADP(+) oxidoreductase, EC 1.1.1.44) is not affected by illumination. 4. These results confirm the idea that illumination results in a switch from the oxidative to the reductive pentose phosphate cycle via light-dependent regulation of glucose-6-phosphate dehydrogenase.