The Function of Ascorbic Acid in Photosynthetic Phosphorylation.
Ascorbate is oxidized to the free radical monodehydroascorbate by O2.- and by H2O2 (through the action of ascorbate peroxidase) formed in the Mehler reaction by isolated spinach (Spinacia oleracea) thylakoids. Light-dependent electron transport from water to monodehydroascorbate is shown to be coupled to ATP formation with a ratio ATP:O2 of 2. In the presence of ascorbate the net O2 exchange balance of the Mehler reaction is close to zero, and the synthesis of ATP is increased 2 to 3 times due to the extra electron transport to the monodehydroascorbate free radical. A scheme of the electron transport in the presence of ascorbate is discussed.
Forti
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Centro di Studio Consiglio Nazionale delle Ricerche sulla Biologia Cellulare e Molecolare delle Piante, Dipartimento di Biologia, Universita di Milano, Via Celoria 26, Milano 20133, Italy.
Elli
G.
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