INTRODUCTION OF A PHOSPHATE AT SERINE(741) OF THE CALMODULIN-BINDING DOMAIN OF THE NEURONAL NITRIC-OXIDE SYNTHASE (NOS-I) PREVENTS BINDING OF CALMODULIN

The calmodulin-binding domain of neuronal nitric oxide synthase (NOS-I ) is represented by a segment of 26 amino acids. We tested whether the phosphorylation of a serine in the calmodulin-binding domain changes the affinity of calmodulin for this binding site. We monitored the bin ding of calmodulin to synthetic peptides by surface plasmon resonance spectroscopy, an electrophoretic mobility assay, circular dichroism sp ectroscopy and competitive inhibitory studies. Ail four experimental a pproaches showed that binding of calmodulin to the calmodulin-binding site is blocked by introduction of a phosphate. Phosphorylation of the calmodulin-binding domain of NOS-I could be a negative feedback loop to turn off NOS-I activity.