Nitric oxide synthase regulatory sites. Phosphorylation by cyclic AMP-dependent protein kinase, protein kinase C, and calcium/calmodulin protein kinase; identification of flavin and calmodulin binding sites

• Published in: The Journal of biological chemistry Vol. 267; no. 16; pp. 10976 - 10981
• Main Authors: BREDT, D. S, FERRIS, C. D, SNYDER, S. H
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 05.06.1992
• Subjects: Affinity Labels; Amino Acid Oxidoreductases - metabolism; Analytical, structural and metabolic biochemistry; Autoradiography; binding; Binding Sites; Biological and medical sciences; Calcium-Calmodulin-Dependent Protein Kinases; calmodulin; Calmodulin - metabolism; Cell Line; Electrophoresis, Polyacrylamide Gel; Enzymes and enzyme inhibitors; flavin; Flavins - metabolism; Fundamental and applied biological sciences. Psychology; identification; Nitric Oxide Synthase; Oxidoreductases; Peptide Mapping; Phosphorylation; Protein Kinase C - metabolism; Protein Kinases - metabolism; sites; Stoichiometry; Phosphorylation; Purification; Rat; Enzyme; Rodentia; Binding site; Vertebrata; Mammalia; Structure activity relation; Second messenger; Nitrogen monoxide; Localization; Brain (vertebrata)
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)49862-1

Nitric oxide (NO) is an important molecular messenger accounting for endothelial-derived relaxing activity in blood vessels, mediating cytotoxic actions of macrophages, and functioning as a neurotransmitter in the brain and periphery. NO synthase (NOS) from brain has been purified to homogeneity and molecularly cloned. We now report that NOS is stoichiometrically phosphorylated by cAMP dependent protein kinase, protein kinase C, and calcium/calmodulin-dependent protein kinase, with each kinase phosphorylating a different serine site on NOS. Activation of PKC in transfected cells reduces NOS enzyme activity by approximately 77% in intact cells and by 50% in protein homogenates from these cells. Utilizing fluorescence spectroscopy we find that purified monomer NOS contains 1 molar equivalent of both FMN and FAD. This stoichiometry is supported by enzymatic digestion of the flavins with phosphodiesterase, and titration of the FMN with a specific FMN binding protein. We demonstrate that purified NOS is labeled by a photoaffinity derivative of calmodulin. These recognition sites on NOS provide multiple means for regulation of NO levels and "cross-talk" between second messenger systems.