Distances between functional sites in cardiac sarcoplasmic reticulum (Ca2+ +Mg2+)-ATPase. Inter-lanthanide energy transfer.
The high-affinity Ca2+-binding sites of cardiac sarcoplasmic reticulum (Ca2+ +Mg2+)-ATPase have been probed using trivalent lanthanide ions. Non-radiative energy-transfer studies, using luminescent probe Eu3+ as a donor and Nd3+ or Pr3+ as acceptor, were carried out to estimate the distance between two high-affinity Ca2+-binding/transport sites. Eu3+ was excited directly with pulsed laser light and the energy-transfer efficiency to Nd3+ or Pr3+ was measured, under the conditions in which most donor-acceptor pairs occupied the high-affinity Ca2+ sites. The distance between two high-affinity Ca2+ sites is about 0.89 nm. In the presence of ATP the distance between the high-affinity sites is about 0.855 nm, whereas in the presence of adenosine 5'-[beta, gamma-methylene]triphosphate or adenosine 5'-[beta, gamma-imino]triphosphate the distance is about 0.895 nm. To estimate the distance between the high-affinity Ca2+ sites and ATP-binding/hydrolytic site, we have measured the energy-transfer efficiency between Eu3+ and Cr3+-ATP with Eu3+ at the high-affinity Ca2+ sites and Cr3+-ATP at the ATP-binding/hydrolytic site. Our results show that ATP-binding/hydrolytic site is separated by about 2.2 nm from each high-affinity Ca2+ site.
Joshi
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NB
Department of Biological Chemistry, University of Maryland, School of Medicine, Baltimore 21201.
Shamboo
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AE
D000818:Animals; D017317:Annexin A6; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004285:Dogs; D004735:Energy Transfer; D008433:Mathematics; D008674:Metals, Rare Earth / Q000378:metabolism* / Q000502:physiology; D009206:Myocardium / Q000201:enzymology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D017317:Annexin A6; D002135:Calcium-Binding Proteins; D008674:Metals, Rare Earth; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases