Biological fate of amino acid, peptide and protein hydroperoxides

In the course of searching for a suitable marker for studying protein oxidation, we have successfully elucidated the structures of three valine hydroperoxides, i.e. β-hydroperoxyvaline, (2S,3S)-γ-hydroperoxyvaline and (2S,3R)-γ-hydroperoxyvaline, which are novel products of protein oxidation. The corresponding valine hydroxides were obtained by sodium borohydride reduction. We hypothesized that valine hydroxides might be the major biological degradation products of valine hydroperoxides and, as such, could be useful markers for the study of protein oxidation in vivo. The aim of this study was to investigate the fate of valine hydroperoxide in selected biological systems by the use of chemiluminescence detection of hydroperoxides and HPLC analysis of O-phthaldialdehyde derivatives of amino acid residues. The degradation of hydroperoxides present on γ-radiolysed solutions of valine, Pro-Val-Gly, or BSA occurred in the presence of: (1) transition metals (Fe²⁺, Fe³⁺, or Cu²⁺), (2) the detoxifying enzyme GSH peroxidase, (3) human plasma, and (4) J774 mouse monocyte macrophage cells. The major degradation product of valine hydroperoxide recovered in each case was found to be a valine hydroxide. These results suggest that valine hydroxide (derived from the hydroperoxide) may well be a useful in vivo marker for studying protein damage under oxidative stress.