Photoregulation of Nicotinamide Adenine Dinucleotide Kinase Activity in Cell-free Extracts

This article gives evidence that NAD kinase activity is controlled by the action of phytochrome. The NADP level rapidly increased in the cotyledons of seedlings of Pharbitis nil strain Violet (a short day plant), when the inductive dark for flowering was interrupted with a 5-minute illumination of red light. Illumination with far red light immediately after illumination with red light counteracted partly the effect of the latter.A partially purified phytochrome preparation from the uppermost internodes including the hook of Pisum sativum var. Alaska contained NAD kinase activity, and this increased greatly on illumination with red light. The effects of red and far red light on NAD kinase activity were reversible. The Km value of NAD kinase in the phytochrome preparation for NAD was 1.84 mm in the dark and 0.90 mm under red light. A broad optimum of the NAD kinase reaction and its photopotentiation appeared in the region of pH 6.6 to 8.6.The NAD kinase activity in a phytochrome preparation from the coleoptiles of Avena sativa was also activated by red light.It was suggested that the Pfr type of phytochrome may contribute to the decrease of the Km value of NAD kinase reaction by causing a conformational alteration of NAD kinase.