Abstract:Nitrate reductase (NR, E. C. 1.6.6.1), which was purified for 500-fold from crude extract of wheat leaves through the Blue-Dexdran Sepharose 4B affinity colume, could be still increased obviously by NR-SF in vitro. The results demonstrated that NR-SF increasedmainly activity of Cytochrome-C reductase (CytcR) in NR complex, but not affected activity of reduced methylviologen-nitrate reductase (MVH-NR). NR-SF was not similar to glutathione (GSH) which ieversed the inhibition of P-chloromercuribenzoate (PCMB) on activity of NR. So that the action of NR-SF was not in protecting sulfhydryl group of NR protein from oxidation alone.