Isolation of cardiac membrane proteolipids by high pressure liquid chromatography. A comparison of reticular and sarcolemmal proteolipids, phospholamban and calciductin.

Membrane-bound phosphorylatable proteolipids were reported to play a role in the regulation of transmembrane Ca2+ fluxes by catecholamines. A generally applicable purification procedure is described by which such proteolipids as the cardiac sarcoplasmic reticulum phospholamban is purified by solvent extraction followed by high pressure liquid chromatography on microparticulate silica. Phospholamban is thereby purified with a yield of 3.37 mg from 100 mg of sarcoplasmic reticulum proteins, significantly higher than that obtained by any of the previously reported procedures. It appeared homogeneous upon dodecyl sulfate-polyacrylamide gel electrophoresis where it is stained by Coomassie blue and detected by autoradiography. The same procedure is applicable to cardiac sarcolemmal calciductin. Both proteolipids exhibit the same Mr 11 000 and pI 3.7 upon two-dimensional gel electrophoresis. Their amino acid compositions are very similar if not identical. This raises the intriguing possibility that phospholamban and calciductin are identical though they obviously belong to different membranes.