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Articles

Light-Induced Conversion of Nicotinamide Adenine Dinucleotide to Nicotinamide Adenine Dinucleotide Phosphate in Higher Plant Leaves ¹

Hideaki Usuda² and Gerald E. Edwards³

James A. Bassham

Institute of Applied Microbiology, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan, Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706, Laboratory of Chemical Biodynamics, University of California, Berkeley, California 94720, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720

Light-induced conversion of NAD to NADP was investigated in higher plants. Upon illumination, conversion of NAD to NADP was observed in intact leaves of wheat and pea following incubation in the dark. This conversion was also observed in mesophyll protoplasts of wheat leaves when they were isolated in the dark or isolated in light and then preincubated in the dark. Chloroplasts isolated from wheat protoplasts prepared in the dark carried out the conversion. The conversion in the mechanically isolated spinach chloroplasts was observed only when they were isolated in the dark from leaves preincubated in darkness.

Sucrose density gradient centrifugation of wheat protoplast extracts and differential centrifugation of protoplast extracts from various plants showed that most of the NAD kinase was localized in the chloroplasts. Therefore, the conversion of NAD to NADP is considered to occur in the chloroplasts. However, with extracts of maize mesophyll protoplasts, the enzyme was localized in the extrachloroplast fraction. The NAD kinase was activated some 30% by illumination of leaves or protoplasts of pea and wheat after preincubation in the dark.

These results suggest that, in general, the light-induced conversion of NAD to NADP occurs in the chloroplast and is catalyzed by photoactivated NAD kinase using photochemically produced ATP.

³ Present address: Botany Department, Washington State University, Pullman, WA 99163.

¹ Supported by the Japan-United States Cooperative Research Program between the Japan Society for the Promotion of Science and National Research Foundation, U. S. A., and by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, and Culture.

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