Protein Transphosphorylation During the Mutual Interaction between Phytochrome A and a Nuclear Isoform of Nucleoside Diphosphate Kinase Is Regulated by Red Light.

The nuclear isoform of nucleoside diphosphate kinase isoenzyme NDPK-I undergoes strong catalytic activation upon its interaction with the active form of phytochrome A (Pfr) in red light. The autophosphorylation or intermolecular transphosphorylation of NDPK-I leads to the formation of phosphoester bonds stable in acidic solution. The phosphate residue of the phosphamide bond in the active center of NDPK-I can also be transferred to serine and threonine residues localized in other proteins, including phytochrome A. Phytochrome A, similarly to NDPK-I, undergoes autophosphorylation on serine and threonine residues and can phosphorylate some potential substrate proteins. The physical interaction between phytochrome A in the Pfr form and NDPK-I results in a significant increase in the kinase activity of NDPK-I. The results presented in this work indicate that NDPK-I may function as a protein kinase regulated by light.