Factors affecting the integrity of high density lipoproteins in the ultracentrifuge.

Because of reported losses of apolipoproteins from high density lipoproteins during ultracentrifugation, we studied several factors that could affect the integrity of these lipoprotein complexes. Alteration of temperature, rotor configuration, and composition of the tubes had little effect on loss of apolipoprotein A-I. Interestingly, the high ionic strengths commonly used in ultracentrifugal isolation of these lipoproteins were associated with the smallest loss of apolipoprotein A-I. Losses increased substantially as the ionic strength of the medium was decreased. After repeated ultracentrifugation, apolipoprotein A-I content of high density lipoproteins approached a limiting value of approximately 65% of the original serum value, but no apolipoprotein A-II was lost. Our results imply that the binding environments of these two apolipoproteins in high density lipoproteins differ. Further, they imply that apolipoprotein A-I may exist in more than one type of environment or in more than one form in high density lipoproteins.