Sulfenic acid formation in human serum albumin by hydrogen peroxide and peroxynitrite.

摘要: Human serum albumin (HSA), the most abundant protein in plasma, has been proposed to have an antioxidant role. The main feature responsible for this property is its only thiol, Cys34, which comprises approximately 80% of total free thiols plasma and reacts preferentially with reactive oxygen nitrogen species. Herein, we show that thiol HSA reacted hydrogen peroxide a second-order rate constant 2.26 M(-1) s(-1) at pH 7.4 37 degrees C 1:1 stoichiometry. formation intermolecular disulfide dimers was not observed, suggesting being oxidized beyond disulfide. With reagent 7-chloro-4-nitrobenzo-2-oxa-1,3-diazol (NBD-Cl), were able detect sulfenic acid (HSA-SOH) from UV-vis spectra adduct. Cys34 confirmed by mass spectrometry using 5,5-dimethyl-1,3-cyclohexanedione (dimedone). Sulfenic also formed exposure peroxynitrite, product reaction between nitric oxide superoxide radicals, absence or presence carbon dioxide. latter suggests can be through radical pathways since following dioxide, peroxynitrite yields carbonate anion remarkably stable, 15% decaying after 2 h under aerobic conditions. glutathione mixed HSA-glutathione determined upon peroxide-treated glutathione. Thus, HSA-SOH serve as intermediate low molecular weight disulfides, are predominant form thiols, present 25% circulating HSA.