Interaction of fatty acids with the calcium-magnesium dependent adenosine triphosphatase from sarcoplasmic reticulum

Abstract

The fluorescence emission spectrum of dansylundecanoic acid is sensitive to the environment and appears at a lower wavelength when the fatty acid is bound to protein than when it is bound to phospholipid. When bound to the (Ca2+-Mg2+)-ATPase of sarcoplasmic reticulum, the emission spectrum can be resolved into separate components assigned to fatty acid bound to protein and to lipid. Efficiency of energy transfer from the tryptophan residues of the ATPase to dansylundecanoic is higher for protein-bound probe than for lipid-bound probe. Fluorescence titrations are consistent with three fatty acid binding sites per ATPase with a Kd of 7 microM, and these sites are postulated to occur at the protein-protein interface in ATPase oligomers. Fatty acid incorporated into the lipid component of the membrane appears to be bound outside the lipid annulus around the protein.

Does intrinsic fluorescence reflect conformational changes in the Ca2+‐ATPase of sarcoplasmic reticulum?

“…Brominated or spin labelled lipophilic quenchers might be useful for this purpose, provided their localization is not uncertain, as is the case, for instance, for fatty acid probes which may bind to non-annular sites on the ATPase [22]. Experiments are in progress along this line.…”

“…In conclusion, the present experiments suggest that studies of tryptophan quenching [lo-12,18-221 could be pursued not only to investigate lipid-protein interactions [20-221 or the depth at which ATPase tryptophans are embedded [lo-121, but also to identify the various tryptophan residues on the basis of their sensitivity to different ligands after selective quenching of other tryptophan residues. Brominated or spin labelled lipophilic quenchers might be useful for this purpose, provided their localization is not uncertain, as is the case, for instance, for fatty acid probes which may bind to non-annular sites on the ATPase [22]. Experiments are in progress along this line.…”

Engineering Lipid Bilayer Membranes for Protein Studies

“…For transport on a large scale, there is endocytosis and exocytosis, that move large molecules or whole organisms inside and outside the cell, respectively [1,18]. Co-transport is the coupled passage of two materials across the cell membrane.…”

The function of G-protein coupled receptors and membrane cholesterol: specific or general interaction?

“…For example, it has been reported that for the nicotinic acetylcholine receptor (which requires cholesterol for its function), cholesterol is proposed to be present at the 'nonannular' sites around the receptor (annular sites are binding sites of lipids in the immediate annulus surrounding the cross sectional area of the membrane protein) [57]. These nonannular sites, initially postulated for Ca 2+ /Mg 2+ -ATPase [58,59], are characterized by occlusion of phospholipids. It has been suggested that the possible locations for the nonannular sites could be either inter-or intramolecular protein interfaces [58].…”