Sinapinic acid can replace ascorbate in the biotin switch assay.

BACKGROUND: Protein S-nitrosation is an important post-translational modification altering protein function. Interaction of nitric oxide with thiols is an active area of research, and is one of the mechanisms by which NO exerts its biological effects. Biotin switch assay is the method, which has been developed to identify S-nitrosated proteins. The major concern with biotin switch assay includes reducing disulfide which may lead to false positives. We report a modification of the biotin switch assay where sinapinic acid is utilized instead of ascorbate to eliminate potential artifacts in the detection of S-nitrosated proteins.
METHODS: The denitrosation ability of sinapinic acid was assessed by monitoring either the NO or NO(2)(-) released by chemiluminescent NO detection or by the griess assay, respectively. DTNB assay was used to compare disulfide reduction by ascorbate and sinapinic acid. Sinapinic acid and ascorbate were compared in the biotin switch detection of S-nitrosoproteins in RAW 264.7 cells+/-S-nitrosocysteine (CysNO) exposure.
RESULTS: We show that sinapinic acid has the ability to denitrosate S-nitrosothiols at pH 7.0 and denitrate plus denitrosate at pHs 8 and 8.5. Unlike ascorbate, sinapinic acid degrades S-nitrosothiols, but it does not reduce disulfide bridges.
CONCLUSIONS: Sinapinic acid denitrosate RSNO and does not reduce disulfides. Thus can readily replace ascorbate in detection of S-nitrosated proteins in biotin switch assay. GENERAL SIGNIFICANCE: The work described is important in view of protein S-nitrosation. In this study we provide an important modification that eliminates artifacts in widely used technique for detecting the S-nitrosoproteome, the biotin switch assay.