Photoactivation of NAD Kinase through Phytochrome: Phosphate Donors and Cofactors

The specificities of phosphate donors and the effects of metal chelating agents and divalent metal ions on NAD kinase activation by phytochrome-far red-absorbing form (Pfr) were examined. ATP was the most efficient phosphorylating agent. Uridine 5′-triphosphate, cytidine 5′-triphosphate (CTP), inosine 5′-triphosphate, and guanosine 5′-triphosphate in this order caused significant phosphorylation in the dark. Under red light, striking photoactivation of NAD kinase was obtained with ATP and subsequently CTP.