An ATPase From Halobacterium Saccharovorum
Report describes purification and determination of subunit structure of membrane-bound adenosinetriphosphatase (ATPase) from archaebacterium Halobacterium saccharovorum.
Hochstein, L. I.↗
Engineering topics
Kristjansson, H.
Publications and source records attributed to Kristjansson, H..
Is the ATPase from halobacterium saccharovorum an evolutionary relic?
The ATP Synthase Complex present in the membranes of mitochondria, chloroplasts or bacteria is composed of 2 sectors: FO, an integral membrane protein consisting of 3 subunits mediating proton translocation across the membrane and F1, the catalytic component composed of 5 non-identical subunits. The apparent early origin of the ATP Synthase Complex, as implied by its ubiquitous distribution, seems inconsistent with its structural and functional complexity and raises the question if simpler versions of the ATP Synthase exist. Such an ATP Synthase has been searched for in various Archaebacteria. A purified halobacterial ATPase activity which possesses certain properties consistent with those of an ATP Synthase but which has a different subunit structure is described.
Hochstein, L. I.↗
Trypsin digestion for determining orientation of ATPase in Halobacterium saccharovorum membrane vesicles
Membranes prepared by low pressure disruption of cells exhibited no ATPase activity in the absence of Triton X-100, although 43% of the total menadione reductase activity was detected. Trypsin digestion reduced menadione reductase activity by 45% whereas ATPase activity was not affected. Disruption of the membrane fraction at higher pressure solubilized about 45% of the ATPase activity. The soluble activity was still enhanced by Triton X-100, suggesting that the detergent, besides disrupting membrane vesicles, also activated the ATPase. The discrepancy in localization of menadione reductase and ATPase activities raised questions regarding the reliability of using a single marker enzyme as an indicator of vesicle orientation.
NASA Center ARC↗
Dicyclohexylcarbodiimide-sensitive ATPase in Halobacterium saccharovorum
Membranes from Halobacterium saccharovorum contained a cryptic ATPase which required Mg(2+) or Mn(2+) and was activated by Triton X-100. The optimal pH for ATP hydrolysis was 9-10. ATP or GTP were hydrolyzed at the same rate while ITP, CTP, and UTP were hydrolyzed at about half that rate. The products of ATP hydrolysis were ADP and phosphate. The ATPase required high concentrations (3.5 M) of NaCl for maximum activity. ADP was a competitive inhibitor of the activity, with an apparent Ki of 50 micro-M. Dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis. The inhibition was marginal at the optimum pH of the enzyme. When the ATPase was preincubated with DCCD at varying pH values, but assayed at the optimal pH for activity, DCCD inhibition was observed to increase with increasing acidity of the preincubation medium. DCCD inhibition was also dependent on time of preincubation, and protein and DCCD concentrations. When preincubated at pH 6.0 for 4 h at a protein:DCCD ratio of 40 (w/w), ATPase activity was inhibited 90 percent.
Kristjansson, H.↗
On archaebacterial ATPase from Halobacterium saccharovorum
The energy transducing ATPase from Halobacterium saccharovorum was studied in order to define the origin of energy transducing systems. The ATPase required high salt concentration (4M NaCl) for activity; activity was rapidly lost when NaCl was below 1 Molar. At low salt concentration, the membrane bound ATPase activity could be stabilized in presence of spermine. However, following solubilization spermine was ineffective. Furthermore, F1 ATPase activity was stabilized by ammonium sulfate even when the NaCl concentration was less than 1 Molar. These studies suggest that stabilization by hydrophobic interactions preceded ionic ones in the evolution of the energy transducing ATPases.
Kristjansson, H.↗