Fig. 4.

Inhibition of Cys reduction by NO in vitro and in vivo.(A) Inhibition of Trx/TrxRed-mediated cystine reduction by NO in the reconstituted system (see Experimental Procedures). NO donor MAHMA (45 and 100 μM) was added before initiation of the reaction with NADPH. (B) NO transiently inhibits Cys reduction in vivo. Cells were treated with 1 mM diamide and/or the indicated amount of NO donor MAHMA. At the indicated time points, aliquots were withdrawn, and thiols were quantified as described in Experimental Procedures. NO added to the reaction after it was stopped did not affect the fluorescence yield (data not shown). Values shown are the means ± SD from three experiments.