Structural properties of sarcoplasmic reticulum Ca2+-ATPase as studied by intrinsic protein fluorescence.

1. From the intrinsic fluorescence spectral properties and fluorescence quenching experiments done with acrylamide and iodide, using native sarcoplasmic reticulum vesicles, purified ATPase and ATPase solubilized with 1% Triton X-100, it is deduced that practically all the fluorescent tryptophanyl residues of this protein belong to a single population showing similar hydrophobic microenvironments. 2. Both acrylamide and iodide seem to be able to penetrate through the sarcoplasmic reticulum membrane. 3. The intrinsic fluorescence of the Ca2+-ATPase due to tryptophan residues probably buried inside the membrane is used as a tool to follow thermotropic changes in membrane fluidity of reconstituted systems.