Interspecies activation of lecithin-cholesterol acyltransferase by apolipoprotein A-I isolated from the plasma of humans, horses, sheep, goats and rabbits.

The abilities of apolipoprotein A-I species isolated from humans, horses, sheep, goats and rabbits to activate purified human lecithin-cholesterol acyltransferase and the enzyme from homologous plasmas and plasma of other mammalian species were compared. Each purified apolipoprotein A-I species was individually incorporated into phosphatidylcholine/cholesterol vesicles by the cholate dialysis method to form proteoliposome common substrates (apolipoprotein A-I/phosphatidylcholine/cholesterol molar ratio of 1:250:12.5) for the enzyme activity assay. All apolipoprotein A-I species tested had the ability, but with different effectiveness, to activate plasma lecithin-cholesterol acyltransferase from their own and other animal species and from purified human lecithin-cholesterol acyltransferase. Horse apolipoprotein A-I was nearly as effective as human apolipoprotein A-I, whereas apolipoproteins A-I from goats, sheep or rabbits were, in descending order, slightly less effective than either horse or human apolipoprotein A-I in activating human plasma lecithin-cholesterol acyltransferase. A similar trend in ability to activate purified human lecithin-cholesterol acyltransferase by these apolipoprotein A-I species was seen, but apolipoprotein A-I from sheep, goats and rabbits was only about 55-65% as effective as human apolipoprotein A-I. In general, apolipoprotein A-I from the same animal species as the lecithin-cholesterol acyltransferase enzyme was a better activator of the enzyme than was apolipoprotein A-I from another animal species. Comparison of lecithin-cholesterol acyltransferase activities of each plasma paired with its own apolipoprotein A-I, which reflects the level of the enzyme in the plasma, revealed descending levels of the enzyme's activity (nmol/h per ml) as follows: humans (98.9 +/- 10.3), horses (90.7 +/- 10.6), sheep (69.9 +/- 9.7), goats (64.9 +/- 9.2) and rabbits (52.0 +/- 6.2). Studies with DEAD-Sepharose columns, gel electrophoresis, and proteoliposome substrates demonstrated that apolipoprotein A-I from these mammalian species are similar in molecular charge and weight and are functionally similar in lecithin-cholesterol acyltransferase activation.