Purification and characterization of a membrane-associated ATPase from Natronococcus occultus, a haloalkaliphilic archaeon

Isolated membranes of the extreme haloalkaliphilic archaeon Natronococcus occultus were able to hydrolyze ATP via an ATPase, which required the presence of Mg2+, high concentrations of NaCl, and a pH value of 9. The native molecular mass of the purified ATPase was 130 kDa and was composed of 74- and 61-kDa subunits. Enzyme activity was specific for the hydrolysis of ATP with slight activity towards GTP, CTP, and ITP. The enzyme required NaCl for maximal activity but Na2SO4 and (NH4)(2)SO4 could substitute. The enzyme showed no activity if Na2SO3 or sodium citrate was substituted for NaC1. The ATPase from N. occultus was inhibited by NBD-Cl, NaN3, and ouabain, and was sensitive to nitrate,vanadate, DCCD, and bafilomycin A(1). It was not inhibited by NEM in contrast to other previously characterized halophile ATPases. The ATPase had a K-M of 0.5 mM and appeared to be non-competitively inhibited by NaN3 with a K-I of 3.1 mM. (C) 2000 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.