The delipidation of brain proteolipid protein by ultrafiltration

It has been very difficult to prepare the apoprotein moiety of brain white matter proteolipid so that it is completely devoid of complex lipids, without suffering aggregation and protein denaturation. The reason is that complex lipids are tightly bound to the proteolipid apoprotein. Using a new ultrafiltration method, we obtained, in a gradual way and in a relatively short time, more than 99% delipidation in water-saturated n-butanol, with and without 0.1 M acetic acid, and recovered up to 86% of the protein with no detectable reducing sugars remaining. The delipidated protein remained in solution and in a relatively nondenatured state for several days. In 2% sodium dodecyl sulfate (SDS)-aqueous media, 90% of the lipids were removed and the yield of recovered protein in solution was near 90%; nearly 6% of the reducing sugars remained in the apoprotein. A higher delipidation was obtained by washing with 0.1 M NaOH. The content of reducing sugars was greater but the protein was less stable. When 10% SDS was employed to dissociate lipid-protein interaction, an almost complete delipidation was obtained and reducing sugars disappeared.