The activation of cultured Raw 264.7 murine macrophages with interferon γ and lipopolysaccharide results in the expression of inducible nitric oxide synthase (i-NOS) and the subsequent production of nitric oxide. In the present study, the i-NOS expressed in these activated cells was characterized for possible post-translational protein modification by endogenous tyrosine protein kinases. Western-blot analysis using phosphotyrosine antibodies revealed that i-NOS was phosphorylated on tyrosine residues and that this was an early event coinciding with the appearance of newly synthesized i-NOS. A brief exposure of activated cells to vanadate, a tyrosine phosphatase inhibitor, significantly increased the level of i-NOS tyrosine phosphorylation, suggesting that tyrosine phosphatases are dynamically involved in the regulation of this process. Vanadate treatment of activated cells also resulted in a rapid increase in enzyme activity, occurring within 5 min of exposure. Taken together, these results demonstrate that tyrosine kinases and phosphatases are involved in the post-translational modification of i-NOS and may potentially play a role in modulating the functional activity of the enzyme in macrophages.
Tyrosine phosphorylation of inducible nitric oxide synthase: implications for potential post-translational regulation
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Jinmei PAN, Kendra L. BURGHER, Ann Marie SZCZEPANIK, Garth E. RINGHEIM; Tyrosine phosphorylation of inducible nitric oxide synthase: implications for potential post-translational regulation. Biochem J 15 March 1996; 314 (3): 889–894. doi: https://doi.org/10.1042/bj3140889
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