6533b838fe1ef96bd12a471e

RESEARCH PRODUCT

Chemical model systems for cellular nitros(yl)ation reactions.

subject

description

S-nitros(yl)ation belongs to the redox-based posttranslational modifications of proteins but the underlying chemistry is controversial. In contrast to current concepts involving the autoxidation of nitric oxide ( • NO, nitrogen monoxide), we and others have proposed the formation of peroxynitrite (oxoperoxonitrate (1-)) as an essential intermediate. This requires low cellular fluxes of 'NO and superoxide ( • O 2 - ), for which model systems have been introduced. We here propose two new systems for nitros(yl)ation that avoid the shortcomings of previous models. Based on the thermal decomposition of 3-morpholinosydnonimine, equal fluxes of • NO and • O 2 - were generated and modulated by the addition of • NO donors or Cu,Zn-superoxide dismutase. As reactants for S-nitros(yl)ation, NADP + -dependent isocitrate dehydrogenase and glutathione were employed, for which optimal S-nitros(yl)ation was observed at nanomolar fluxes of • NO and • O 2 - at a ratio of about 3:1. The previously used reactants phenol and diaminonaphthalene (C- and N-nitrosation) demonstrated potential participation of multiple pathways for nitros(yl)ation. According to our data, neither peroxynitrite nor autoxidation of • NO was as efficient as the 3 • NO/1 • O 2 - system in mediating S-nitros(yl)ation. In theory this could lead to an elusive nitrosonium (nitrosyl cation)-like species in the first step and to N 2 0 3 in the subsequent reaction. Which of these two species or whether both together will participate in biological S-nitros(yl)ation remains to be elucidated. Finally, we developed several hypothetical scenarios to which the described • NO/ • O 2 - flux model could apply, providing conditions that allow either direct electrophilic substitution at a thiolate or S-nitros(yl)ation via transnitrosation from S-nitrosoglutathione.