2-Oxo-histidine as a novel biological marker for oxidatively modified proteins.

We report a promising finding that oxidative modification of proteins by free radicals could be monitored by the formation of oxidized histidine that is detectable by reverse-phase HPLC with electrochemical detection (HPLC-ECD). When the N-protected histidine derivative (N-benzoylhistidine) was exposed to a free radical-generating system (copper/ascorbate), a number of products were detected by HPLC-ECD and the main product among them was found to be identical to N-benzoyl-2-oxo-histidine. The acid hydrolysis of N-benzoyl-2-oxo-histidine provided a single product (2-oxo-histidine) that was detected sensitively by HPLC-ECD. Thus 2-oxo-histidine was indeed generated as the main product in the oxidatively modified proteins by free radicals. Taken together, 2-oxo-histidine may be a useful biological marker for assessing protein modifications under oxidative stress.