Isolation and identification of phospholipids of bovine rhodopsin

Phospholipids present in digitonin solutions of bovine rhodopsin have been identified and assayed. Digitonin interferes with extraction of lipids by the usual methods; digitonin was therefore removed from the preparation as an ergosterol digitonide, soluble in absolute ethanol but precipitated in 80% ethanol. The supernatant 80% ethanol contained one portion of the phospholipid, mainly choline and ethanolamine phosphoglycerides with traces of serine phosphoglyceride and sphingomyelin. The rhodopsin residue (free from digitonin) was extracted with chloroform-methanol 2:1; this extract contained the rest of the phospholipid, which consisted only of choline and ethanolamine phosphoglycerides. Plasmalogens were not found, but could have decomposed during the procedures.