Vincenzo Bocchini, Francesca Catanzano, Paolo Arcari, Luciano Masullo, Mariorosario Masullo, Arcari, Paolo, Masullo, L, Masullo, M, Catanzano, F, Bocchini, Vincenzo, Masullo, L., Masullo, M., Catanzano, F., and Bocchini, V.
A NAD(P)H oxidase has been isolated from the archaeon Sulfolobus solfataricus. The enzyme is a homodimer with M r 38,000 per subunit (SsNOX38) containing 1 FAD molecule/subunit. It oxidizes NADH and, less efficiently, NADPH with the formation of hydrogen peroxide. The enzyme was resistant against chemical and physical denaturating agents. The temperature for its half-denaturation was 93 and 75 °C in the absence or presence, respectively, of 8m urea. The enzyme did not show any reductase activity. TheSsNOX38 encoding gene was cloned and sequenced. It accounted for a product of 36.5 kDa. The translated amino acid sequence was made of 332 residues containing two putative βαβ-fold regions, typical of NAD- and FAD-binding proteins. The primary structure of SsNOX38 did not show any homology with the N-terminal amino acid sequence of a NADH oxidase previously isolated from S. solfataricus (SsNOX35) (Masullo, M., Raimo, G., Dello Russo, A., Bocchini, V. and Bannister, J. V. (1996) Biotechnol. Appl. Biochem. 23, 47–54). Conversely, it showed 40% sequence identity with a putative thioredoxin reductase from Bacillus subtilis, but it did not contain cysteines, which are essential for the activity of the reductase.