The enzyme NADH oxidase (EC 220.127.116.11) has been isolated from the two thermoacidophilic archaea Sulfolobus acidocaldarius and Sulfolobus solfataricus and characterized. In both organisms the enzyme oxidizes specifically β-NADH in the presence of molecular oxygen and requires the presence of a flavin cofactor, showing a high specificity for FAD. A stoicheiometric amount of hydrogen peroxide to NADH is formed as the end product of the reaction, indicating that both enzymes are two-electron donors. The purified enzymes exhibit quite different molecular properties. S. acidocaldarius NADH oxidase is a monomeric protein with an estimated molecular mass of about 27 kDa, whereas S. solfataricus NADH oxidase is a dimeric protein with a molecular mass of 35 kDa per subunit; S. solfataricus NADH oxidase is purified as an FAD-containing protein, whereas S. acidocaldarius NADH oxidase does not contain a flavin molecule. Furthermore, a comparison of the N-terminal amino acid sequence shows no similarities either between the two proteins or to any other NADH oxidases. Both enzymes are essentially thermophilic. In the temperature range 20-80°C, the energy of activation is almost the same for both activities, suggesting that similar energetic parameters are required. Also both oxidases display a great stability to heat. The half-life of heat inactivation is about 180 min at 90°C for S. acidocaldarius NADH oxidase and 77 min at 98°C for the S. solfataricus enzyme. The activity of the two enzymes is inhibited by urea and guanidine and are regulated very differently by several organic solvents.
|Number of pages||8|
|Journal||Biotechnology and Applied Biochemistry|
|Publication status||Published - 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)