Cloning and characterization of antioxidant enzyme methionine sulfoxide-S-reductase from Caenorhabditis elegans

Abstract

Methionine (Met) residues in proteins are susceptible to oxidation. The resulting methionine sulfoxide can be reduced back to methionine by methionine, sulfoxide-S-reductase (MsrA). The MsrA gene, isolated front Caenorhabditis elegans was cloned and expressed in Escherichia coli. The resultant enzyme Was able to revert both free Met and Met in proteins in the presence of either NADPH or dithiothreitol (DTT). However, approximately seven times higher enzyme activity was observed in the presence of DTT than of NADPH. The enzyme had an absolute specificity for the reduction Of L-methionine-S-sulfoxide but no specificity for the R isomer. K-m and k(cat) values for the enzyme were similar to1.18 mM and 3.64 min(-1), respectively. Other kinetics properties of the enzyme were also evaluated. (C) 2004 Elsevier Inc. All rights reserved.