Light-Induced Conversion ofNicotinamide Adenine Dinucleotide toNicotinamide Adenine Dinucleotide Phosphate inHigher Plant

Light-induced conversion ofNAD toNADP wasinvestigated inhigher plants. Uponillumination, conversion ofNAD toNADP wasobserved in intact leaves ofwheatandpeafollowing incubation inthedark. This conversion wasalsoobserved inmesophyil protoplasts ofwheatleaves whenthey wereisolated inthedarkorisolated inlight andthenpreincubated inthedark. Chloroplasts isolated fromwheat protoplasts prepared inthedarkcarried outtheconversion. Theconversion inthemechanicafly isolated spinach chloroplasts wasobserved only whenthey wereisolated in thedarkfromleaves preincubated indarkness. Sucrose density gradient centrifugation ofwheatprotoplast extracts anddifferential centrifugation ofprotoplast extracts fromvarious plants showed that mostoftheNAD kinase waslocalized inthechioroplasts. Therefore, theconversion ofNAD toNADPisconsidered tooccur inthe chloroplasts. However, withextracts ofmaizemesophyll protoplasts, the enzyme waslocaized intheextrachloroplast fraction. TheNAD kinase wasactivated some30%bylumination ofleaves orprotoplasts ofpeaand wheat after preincubation inthedark. Theseresults suggest that, ingeneral, thelight-induced conversion of NADtoNADPoccurs inthechloroplast andiscatalyzed byphotoactivated NADkinase using photochemicaMy produced ATP.