Kinetics of Activation of Nicotinamide Adenine Dinucleotide Kinase by Phytochrome—Far Red-absorbing Form

The effects of exogenous redox cofactors and purine analogues on the activation of the NAD kinase by Pfr were examined. Addition of phenazine methosulfate, flavin mononucleotide, or methylene blue increased the activation of NAD kinase by red light in a partially purified preparation of phytochrome. Phenazine methosulfate and flavin mononucleotide do not absorb light in the red or far red region, so they do not act as light receptors in this activation. Thus they probably intervene in electron transfer between phytochrome and NAD kinase. Addition of kinetin with these compounds increased photopotentiation further. In the presence of phenazine methosulfate and kinetin, the activation of NAD kinase by red light was counteracted by illumination with far red light immediately after red light.The relation between the dose of illumination with red light and the degree of activation of NAD kinase was measured. Illumination for 5 minutes with 800 ergs cm(-2) sec(-1) of red light was sufficient to obtain maximal activation. In the dark, the activated state of NAD kinase was maintained for about 10 min and then rapidly lost. The time of preservation of the activated state was greatly shortened by illumination with far red light, indicating the participation of phytochrome.