Michael Hinrichs, Günter Schäfer, Stefan Anemüller
Functional Characterization of an Extremely Thermophilic
ATPase in Membranes of the Crenarchaeon Acidianus
ambivalens
A plasma membrane-bound adenosine triphosphatase
with specific activities up to 0.2 ?mol min?1
(mg protein)?1 at 80°C was detected in the thermoacidophilic
crenarchaeon Acidianus ambivalens (DSM
3772). The enzymatic activity exhibited a broad pH-optimum
in the neutral range with two suboptima at
pH 5.5 and 7.0, respectively. Sulfite activation resulted
in only one pH optimum at 6.25. In the presence of the
divalent cations Mg2+ and Mn2+ the ATPase activity
was maximal. Remarkably, the hydrolytic rates of GTP
and ITP were substantially higher than for ATP. ADP
and pyrophosphate were only hydrolyzed with small
rates, whereas AMP was not hydrolyzed at all. Both
activities could be weakly inhibited by the classical F-type
ATPase inhibitor N, N?dicyclohexylcarbodiimide,
whereas azide had no influence at all. The classical inhibitor
of V-type ATPases, nitrate, also exerted a small
inhibitory effect. The strongly specific V-type ATPase
inhibitor concanamycin A, however, showed no effect
at all. The P-type ATPase inhibitor vanadate had no inhibitory
effect on the ATPase activity at pH 7.0, whereas
a remarkable inhibition at high concentrations
could be observed for the activity at pH 5.5. Arrhenius
plots for both membrane bound ATPase activities
were linear up to 95°C, reflecting the enormous thermostability
of the enzyme.
Biological Chemistry, Walter de Gruyter
Print ISSN: 1431-6730
Volume: 380, 09/1999
Pages: 1063 - 1069
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