Enzymatic reduction of protein-bound methionine sulfoxide.

An enzyme that catalyzes the reduction of methionine sulfoxide residues in ribosomal protein L12 has been partially purified from Escherichia coli extracts. Methionine sulfoxide present in oxidize Metenkephalin is also reduced by the purified enzyme. The enzyme is different from a previously reported E. coli enzyme that catalyzes the reduction of methionine sulfoxide to methionine Ejiri, S. I., Weissbach, H. & Brot, N. (1980) Anal. Biochem. 102, 393--398. Extracts of rat tissues, Euglena gracilis, Tetrahymena pyriformis, HeLa cells, and spinach also can catalyze the reduction of methionine sulfoxide residues in protein.