Enzymatic reduction of methionine sulfoxide residues in proteins and peptides

Abstract

This chapter describes the purification and characteristics of an enzymatic system from Escherichia coli and human leukocytes that specifically reduces methionine sulfoxide, Met(O), residues in proteins and peptides to methionine. This enzymatic reduction can restore the biological activity of an inactive oxidized protein or peptide. In earlier studies, the assay for the presence of an enzyme, Met(O)-peptide reductase, capable of reducing Met(O) residues in proteins utilized oxidized E. coli ribosomal protein L12 as substrate. This assay is long and cumbersome and the substrate is not readily available. Because it has now been established that Met(O)-enkephalin could serve as a substrate, other Met(O)-containing compounds were tested in the study presented in the chapter. One of these, N-acetylMet(O), was found to be a good substrate and the product of the reaction, N-acetylMet, could be rapidly quantitated. The chapter shows the effect of protein concentration on the synthesis of N-acetylmethionine. The rate of reduction of N-acetylMet(O) by Met(O)-peptide reductase increases linearly with protein concentration.