The membrane-bound NADH dehydrogenase of an alkaliphilic Bacillus YN-1 involved in the respiratory chain exhibits reductase activity for hydrogen peroxide and cumene hydroperoxide in the presence of the 22-kDa component (AhpC) from Amphibacillus xylanus (Koyama et al. Biochem. Biophys. Res. Commun. 247, 659-662). In this study, AhpC-like polypeptide with an apparent molecular mass of 20 kDa was isolated from the cell-free extract of YN-1. The NADH dehydrogenase exhibited reductase activity for cumene hydroperoxide in the presence of the purified AhpC-like component from YN-1. It is likely that the NADH dehydrogenase is not only involved in the respiratory chain, but also functions for scavenging peroxide in the presence of its own endogenous AhpC component. The enzyme expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST) showed the NADH dehydrogenase activity as high as the native enzyme from YN-1. While the fusion protein was unable to reduce cumene hydroperoxide in the presence of AhpC-like protein from YN-1, the protein obtained by the cleavage treatment of the fusion protein to release CST exhibited the reductase activity as much as the native enzyme.