The effect of NO on phosphotyrosine protein phosphatases (PTPases) has been investigated in vivo. NO production is induced in interferon-γ and lipopolyaccharide stimulated RAW-264.7 macrophages as indicated by the increase of NO2 − in the medium. Our results demonstrate an inhibition of p-nitrophenylphosphatase activity as a consequence of macrophages activation. Under the described experimental conditions, most of the hydrolysis of p-nitrophenylphosphate can be ascribed to the action of cellular PTPases. The presence of 01120-4/asset/equation/feb20014579395011204-math-si1.gif?v=1&s=becf99a460880a7e5c5e7330fbbe74aa14eed30c)
, a specific inhibitor of NO synthase decreases the inactivation rate of both membrane-bound and soluble PTPases. This evidence further confirms the ability of NO to inactivate PTPases and suggests a possible role of NO in the regulation of cellular processes involving this class of phosphatases.
