NAD Kinase in Higher Plants

NAD kinase was exclusively found in the soluble portion of the cell components. The enzyme was purified about 100-fold from sucrose extracts of spinach leaves.Plant NAD kinase catalyzes formation of NADP from NAD, ATP, and Mg(++), but scarcely any formation of NADPH from NADH. NADH was a very potent competitive inhibitor of NAD phosphorylation by plant NAD kinase. The K(i) was 1.0 x 10(-4)m.The concentration of Mg(++) required to produce maximal activity was 10(-2)m. Co(++) or Mn(++) could replace Mg(++) in the system.The pH optimum was 6.8. The K(m) for NAD was 2.0 x 10(-3)m and that for ATP was 1.1 x 10(-3)m. No convincing demonstration of the reversibility of the reaction was obtained.It was inferred from above properties of the enzyme that NADP formation ceases in plant tissues in which reduced NAD is accumulated, or in anaerobic tissues.

Variation of nicotinamide adenine dinucleotide phosphate level in bean hypocotyls in relation to o(2) concentration

Slices of hypocotyls from 3-day-old seedlings of Vigna sesquipedalis (L.) Fruwirth in the germination stage were incubated under various gaseous conditions. The NADP+NADPH level in the hypocotyl slices changed with the oxygen tension. A high NADP+NADPH level was observed under aerobic conditions and a low NADP+NADPH level under anaerobic conditions.The 100 x NADH/NAD+NADH ratio increased greatly under anaerobic conditions. In general a low NADP + NADPH level corresponded with a high 100 x NADH/NAD+NADH ratio. On the basis of the results given in the following paper, it was discussed that the slowness of NADH oxidation in hypocotyl tissue due to anaerobic conditions results in the inhibition of NADP formation.The variation of the NADP+NADPH level was considered to produce a modification of the carbohydrate metabolism.The NADP+NADPH level in E. coli cells suspended in glucose solution also changed with the oxygen tension.