NMR relaxation measurements detect four intermediate states of ATPase and transport cycle of sarcoplasmic reticulum Ca2+-ATPase.
At least four of the intermediate states of Ca2+-ATPase (and presumably ion transport) can be trapped and characterized using water proton relaxation measurements. Gd3+ binds to two occluded Ca2+ transport sites on Ca2+-ATPase which have a low accessibility to solvent water. In the presence of the MgATP analogue Co(NH3)4AMPPCP, a new state for bound Gd3+ with one less water of hydration) is observed. In the presence of Co(NH3)4ATP or ATP, two additional states for bound Gd3+ are detected by NMR, the first of which probably represents an intermediate state of ATP hydrolysis. The latter is the most occluded Gd3+ site yet observed in these studies and corresponds to the highly occluded E1-P state observed with CrATP (Vilsen and Andersen, Biochim. Biophys. Acta 898, 313 (1987).
Klemens
M R
MR
Department of Chemistry, University of Virginia, Charlottesville 22901.
Grisham
C M
CM
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives; D001692:Biological Transport; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification* / Q000378:metabolism; D006868:Hydrolysis; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008674:Metals, Rare Earth; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013379:Substrate Specificity
D046911:Macromolecular Substances; D008674:Metals, Rare Earth; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases