PROTEOLYTIC DIGESTION OF BOVINE BRAIN WHITE MATTER PROTEOLIPID

—Proteolipids were previously considered to be resistant to proteolytic digestion. In the present study, crude bovine white matter proteolipid, proteolipid apoprotein, and chemically modified proteolipids were subjected to the action of the following proteolytic enzymes in the absence and presence of detergents: trypsin, α-chymotrypsin, elastase, thermolysin and collagenase. The course of digestion was followed by the release of Fluorescamine-reactive groups. Tryptic digestion of the crude proteolipid and the apoprotein in the absence of detergent amounted to 10 and 40% respectively of the digestion in the presence of detergent. Peptide mapping and protein analyses of both the soluble digests and the insoluble residues confirmed digestion. In the presence of either sodium deoxycholate or Triton X-100, essentially all of the crude proteolipid and 60% of the proteolipid apoprotein were solubilized by trypsin. Digestion of the apoprotein was observed only in preparations which had not been dried. In the absence of detergent, (1) the oxidized crude proteolipid was more susceptible to tryptic digestion than were either the unoxidized or carboxymethylated preparations, (2) both the apoprotein and the oxidized proteolipid were digested by thermolysin or α-chymotrypsin, and (3) all preparations were attacked by elastase.