Transmembrane nitration of hydrophobic tyrosyl peptides - Localization, characterization, mechanism of nitration, and biological implications

We have shown previously that peroxynitrite-induced nitration of a hydrophobic tyrosyl probe is greater than that of tyrosine in the aqueous phase (Zhang, H., Joseph, J., Feix, J., Hogg, N., and Kalyanaraman, B. (2001) Biochemistry 40, 7675-7686). In this study, we have tested the hypothesis that the extent of tyrosine nitration depends on the intramembrane location of tyrosyl probes and on the nitrating species. To this end, we have synthesized membrane spanning 23-mer containing a single tyrosyl residue at positions 4, 8, and 12. The location of the tyrosine residues in the phospholipid membrane was determined by fluorescence and electron spin resonance techniques. Nitration was initiated by slow infusion of peroxynitrite, co-generated superoxide and nitric oxide ((NO)-N-.), or a myeloperoxidase/hydrogen peroxide/nitrite anion (MPO/H2O2/NO2-) system. Results indicate that with slow infusion of peroxynitrite, nitration of transmembrane tyrosyl peptides was much higher (10-fold or more) than tyrosine nitration in aqueous phase. Peroxynitrite-dependent nitration of tyrosyl-containing peptides increased with increasing depth of the tyrosyl residue in the bilayer. In contrast, MPO/H2O2/ NO2--induced tyrosyl nitration decreased with increasing depth of tyrosyl residues in the membrane. Transmembrane nitrations of tyrosyl-containing peptides induced by both peroxynitrite and MPO/H2O2/NO2- were totally inhibited by (NO)-N-. that was slowly released from sperimine NONOate. Nitration of peptides in both systems was concentration-dependently inhibited by unsaturated fatty acid. Concomitantly, an increase in lipid oxidation was detected. A mechanism involving (NO2)-N-. radical is proposed for peroxynitrite and MPO/H2O2/NO2- -dependent transmembrane nitration reactions.