Effects of Combined Phosphorylation at Ser-617 and Ser-1179 in Endothelial Nitric-oxide Synthase on EC50(Ca2+) Values for Calmodulin Binding and Enzyme Activation

Abstract

We have investigated the possible biochemical basis for enhancements in NO production in endothelial cells that have been correlated with agonist-or shear stress-evoked phosphorylation at Ser-1179. We have found that a phosphomimetic substitution at Ser-1179 doubles maximal synthase activity, partially disinhibits cytochrome c reductase activity, and lowers the EC 50 (Ca 2 ) values for calmodulin binding and enzyme activation from the control values of 182 2 and 422 22 nM to 116 2 and 300 10 nM. These are similar to the effects of a phosphomimetic substitution at Ser-617 (Tran, Q. K., Leonard, J., Black, D. J., and Persechini, A. (