Sulfur-to-nitrogen transnitrosation: transfer of nitric oxide from S-nitroso compounds to diethanolamine and the role of intermediate sulfur-to-sulfur transnitrosation.

S-Nitrosothiols are formed in vivo and are involved in NO signaling. We investigated the sulfur-to-nitrogen transnitrosation activity of S-nitrosocysteine, S-nitrosoglutathione, S-nitrosohomocysteine, S-nitrosocysteinylglycine and S-nitroso-N-acetylcysteine in their reaction with the secondary amine diethanolamine in vitro. The resulting N-nitrosodiethanolamine, a strong carcinogen, was formed in yields of up to 11% from S-nitrosocysteine and S-nitrosocysteinylglycine, whereas the transnitrosation activity of the other S-nitroso compounds was weak. However, the addition of L-cysteine to a solution of S-nitrosohomocysteine and diethanolamine accelerated the decomposition of S-nitrosohomocysteine and resulted in a significant formation of N-nitrosodiethanolamine accompanied by the intermediate generation of S-nitrosocysteine. Thus, reactive nitrosothiols can be formed from less reactive analogs via sulfur-to-sulfur transnitrosation. We suggest that this affects regulation of NO trafficking in vivo. The reaction provides an alternative mechanism for the generation of carcinogenic N-nitroso derivatives.