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 [rabbit muscle] 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 densylundecanoic is higher for protein-bound probe than for lipid-bound probe. Fluorescence titrations are consistent with 3 fatty acid binding sites/ATPase with a Kd of 7 .mu.M, 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.