Reversible transformation of precipitated and nonprecipitated lipoproteins recombined from proteins and lipids of erythrocyte membranes

The sedimentation at low speed centrifugation of a lipoprotein recombined from the lipids and the strongly bound proteins of the human erythrocyte membrane depends on pH: between 4.5 and 6.0, most of the liproprotein sediments, whereas at pH 7.0-8.5, up to 90% remains in the supernatant. Precipitation of the lipoprotein can be reversed by increasing the pH, followed by a brief sonication. The mobility of spin-labelled protein groups in the lipoprotein increases with increasing pH. This mobility increase is also reversible and is of equal magnitude in precipitated and nonprecipitated recombinates. It is concluded that, because of these reversibilities, determination of the yield of liproprotein formation in recombination experiments must include analysis of both precipitated and nonprecipitated lipoproteins