Spinach chloroplasts were immobilized in 2% agar gel. Crude ferredoxin and NADP–ferredoxin oxidoreductase isolated from spinach were used as electron carriers. The activity of the NADP reduction by immobilized chloroplasts increased with increasing ferredoxin concentration and the maximum activity was obtained at 8μM ferredoxin. The saturation of NADP reduction was observed at a light intensity of over 1000 lx. The optimum pH and temperature of NADP reduction were 8 and 25°C, respectively. The reduced NADP in a reaction medium increased linearly with increasing reaction time under illumination. NADP was continuously reduced for 2 hr with a hollow‐fiber reactor containing immobilized chloroplasts. NADPH and NADP were separated with a hollow‐fiber dialyzer from ferredoxin and NADP–ferredoxin oxidoreductase, which were reused. The conversion ratio of NADP to NADPH was from 40 to 80%.
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