[Localization of tryptophan residues in Ca2+-ATPase from sarcoplasmic reticulum]

By the methods of spectroscopy, fluorimetry and chemical modification of tryptophane residues with N-bromsuccinimide, the sarcoplasmic reticulum of rabbit sceletal muscle was shown to contain 18 +/- 1 tryptophane residues per Ca2+-ATPase molecule, 6 of which were, probably, inside the protein globule, in its hydrophobic region, and thus unavailable for modifier, while the rest 12 +/- 1 were easily transformed to the 6-oxyindole chromophore being the main source of the intrinsic fluorescence of the enzyme. The quantum yield for the rest four residues was equal to 0.015. Four tryptophane residues are located at the distance of less than 14 A from the ATP-binding site of the enzyme. The quantum yields of fluorescence for 8 of the tryptophane residues of Ca2+-ATPase were similar and equal to 0.03.