NADH peroxidase activity of rubrerythrin

P. S. Alban et al. (J. Appl. Microbiol. (1998) 85, 875-882) reported that a mutant H2O2-resistant strain of Spirullum (S.) volutans showed constitutive overexpression of a protein whose amino acid sequence and molecular weight closely resembled that of a subunit of rubrerythrin, a non-heme iron protein with no known function. They also reported that the mutant strain, but not the wild-type, showed NADH peroxidase activity. Here we demonstrate that rubrerythrin and nigerythrin from Desulfovibrio vulgaris and rubrerythrin from Clostridium perfringens show NADH peroxidase activities in an in vitro system containing NADH, hydrogen peroxide, and a bacterial NADH oxidoreductase. The peroxidase specific activities of the rubrerythrins with the "classical" heme peroxidase substrate, o-dianisidine, are many orders of magnitude lower than that of horseradish peroxidase. These results are consistent with the phenotype of the H2O2-resistant strain of S. volutans. The reaction of reduced (i.e., all-ferrous) rubrerythrin with excess O2 takes several minutes, whereas the anaerobic reaction of reduced rubrerythrin with hydrogen peroxide is on the millisecond time scale and results in full oxidation of all iron centers to their ferric states. Rubrerythrins could, thus, function as the terminal components of NADH peroxidases in air-sensitive bacteria and archaea.