PURIFICATION AND CHARACTERIZATION OF SPOROLACTOBACILLUS-INULINUS NADHOXIDASE AND ITS PHYSIOLOGICAL-ROLE IN AEROBIC METABOLISM OF THE BACTERIUM

NADH oxidase was purified to homogeneity from aerobic cells of Sporola ctobacillus inulinus. The N-terminal amino acid sequence showed high s imilarity to those of the NADH oxidase from Amphibacillus xylanus and the H2O2-forming NADH oxidase from Streptococcus mutans. S. inulinus N ADH oxidase is a homodimer composed of subunits and with a molecular m ass of 53 kDa, It catalyzes the reduction of oxygen to hydrogen peroxi de, and, in the presence of a low molecular weight disulfide-containin g component (AhpC) from A. xylanus, of hydrogen peroxide to water, The V-max values for hydrogen peroxide and cumene hydroperoxide reduction were 9,300 and 8,500 min(-1), respectively at 25 degrees C. These val ues are similar to the V-max values for hydrogen peroxide and cumene h ydroperoxide reduction with the NADH oxidase from A. xylanus. Cell ext racts from S. inulinus cultures grown under anaerobic and aerobic cond itions reacted with antibodies against the AhpC protein from A. xylanu s. An immunoreactive AhpC-like 21 kDa protein was induced in S. inulin us under aerobic, but not under anaerobic conditions, The results sugg est that AhpC is involved in the aerobic metabolism of S. inulinus, wh ich lacks a respiratory chain and catalase. The AhpC-NADH oxidase syst em is thought to function as a scavenging system for hydrogen peroxide formed aerobically.