* To whom correspondence should be addressed.
Received May 25, 2016; Revision received June 30, 2016
The nuclear isoform of nucleoside diphosphate kinase isoenzyme NDPK-In 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-In leads to the formation of phosphoester bonds stable in acidic solution. The phosphate residue of the phosphamide bond in the active center of NDPK-In can also be transferred to serine and threonine residues localized in other proteins, including phytochrome A. Phytochrome A, similarly to NDPK-In, 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-In results in a significant increase in the kinase activity of NDPK-In. The results presented in this work indicate that NDPK-In may function as a protein kinase regulated by light.
KEY WORDS: nucleoside diphosphate kinase, phytochrome, signal transduction, transphosphorylation