Decreased S-nitrosation of peptide thiols in the membrane interior.

It has been proposed that autoxidation of nitric oxide (()NO) stimulates S-nitrosation of thiols located in the hydrophobic milieu. We tested whether thiols located in hydrophobic membranes undergo enhanced S-nitrosation in the presence of ()NO/O(2). The transmembrane cysteinyl peptides C(4) (AcNH-KKACALA(LA)(6)KK-CONH(2)) and C(8) (AcNH-KKALALACALA(LA)(3)KK-CONH(2)) were incorporated into dilauroylphosphatidylcholine bilayers; their location in the membrane was determined by EPR spin labeling. The peptides, C(8) and C(4), and glutathione (GSH; 300 microM) were treated with a ()NO donor, DEA-NONOate, and nitrosothiol formation was determined under various O(2) levels. Surprisingly, the more hydrophobic cysteinyl peptide, C(8), did not yield any S-nitrosated product compared to GSH in the aqueous phase or C(4) peptide in the liposomes in the presence of ()NO/O(2). These data suggest that thiols located deeply in the hydrophobic core of the membrane may be less likely to undergo S-nitrosation in the presence of ()NO/O(2).