Post-translational regulation of nitrate reductase activity: A role for Ca2+ and 14-3-3 proteins

The control of nitrate reductase (NR) activity by reversible protein phosphorylation is a two-stage process: the enzyme is reversibly phosphorylated, and the phosphorylated form then binds an inhibitor protein. Recent results indicate that the phosphorylation reaction is Ca2+-dependent and that the inhibitor is a member of the 14-3-3 family of proteins. These results suggest the convergence of several signal transduction pathways in the control of nitrate assimilation. Recent results also implicate metabolites and 5'-AMP as possible effecters regulating the phosphorylation status of NR in vivo.