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Annular and non-annular binding sites on the ( Ca 2+ + Mg 2+)- ATPase

Authors
  • Simmonds, A.C.
  • East, J.M.
  • Jones, O.T.
  • Rooney, E.K.
  • McWhirter, J.
  • Lee, A.G.
Type
Published Article
Journal
Biochimica et Biophysica Acta (BBA) - Biomembranes
Publisher
Elsevier
Publication Date
Jan 01, 1982
Volume
693
Issue
2
Pages
398–406
Identifiers
DOI: 10.1016/0005-2736(82)90447-3
Source
Elsevier
Keywords
License
Unknown

Abstract

Quenching of the fluorescence of the ( Ca 2+ + Mg 2+)- ATPase purified from muscle sarcoplasmic reticulum can be used to measure relative binding constants of hydrophobic compounds to the phospholipid-protein interface. We show that the binding constant for cholesterol is considerably less than that for phosphatidylcholine, so that cholesterol is effectively excluded from the phospholipid annulus around the ATPase. However, dibromocholestan-3β-ol causes quenching of the fluorescence of the ATPase, and so has access to other, non-annular sites. We suggest that these non-annular sites could be at protein/protein interfaces in ATPase oligomers. Oleic acid can bind at the phospholipid/protein interface, although its binding constant is less than that for a phosphatidylcholine, and it can also bind at the postulated non-annular sites. The effects of these compounds on the activity of the ATPase depend on the structure of the phospholipid present in the systems.

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