Isolation of the fundamental polypeptide subunits of biological membranes

A group of peptides (some or all of them glycopeptides), of molecular weight about 5000, has been shown to be a major fraction of biological membranes. These "miniproteins" have been prepared from membranes of human and bovine red blood cells, from purified bovine liver mitochondria, and from the rhodopsin-containing membranes of the outer segments of bovine retinal rods. While the miniproteins were found in large amounts in each case, the other protein components differed markedly depending on the function of the membrane studied. This fact was particularly clear in the case of the rod membranes where the only major proteins detected were the miniproteins and rhodopsin. The large size of the miniprotein fraction in each of these membranes leads us to propose that the miniproteins play a fundamental role in the several functions which occur as common denominators in biological membranes.