High density lipoprotein subfraction-1 (
HDL(1)) is thought to interact with the high-affinity
apoprotein B, E receptors of peripheral cells and may act as a modulator of
LDL binding and uptake. In the present study the concentration and composition of
HDL(1) in normal and hypercholesterolemic sera were studied using
zonal ultracentrifugation. To permit separation of the
HDL(1) from VLDL,
LDL, and Lp(a), the
apoB-containing
lipoproteins were first precipitated from serum using the
phosphotungstic acid/
magnesium chloride (PTA/MgCl(2)) method after which the supernatant fraction was subjected to
zonal ultracentrifugation. It could be demonstrated that following PTA/MgCl(2) precipitation
HDL(1) floats as a single peak at d 1.08-1.09 g/ml (NaBr) and is sufficiently separated from
high density lipoprotein-2 (
HDL(2)) and
high density lipoprotein-3 (HDL(3)). The
HDL(2)/HDL(3) subfraction pattern was not affected by the precipitation method. As previously described, in vitro incubation of serum leads to the LCAT-dependent interconversion of HDL(3) or
HDL(2). Using the technique described here, it was discovered that a simultaneous elevation of
HDL(1) occurred. This increase in
HDL(1) concentration could not be observed when LCAT was inhibited by heat inactivation or addition of
Ellman's reagent. In normal fresh serum only a small
HDL(1) peak could be detected, but in patients with
familial hypercholesterolemia (
apoB, E receptor deficiency)
HDL(1) was elevated five to tenfold compared to normal values and further increased in concentration upon incubation of serum. On the other hand, in sera of patients with familial HDL deficiency (
Tangier disease),
HDL(1) was undetectable. Analysis of the HDL fractions in serum of a patient with
abetalipoproteinemia revealed that following in vitro incubation there was formation of
HDL(1) despite the lack of
apoprotein B-containing
lipoproteins. These data support the concept that
HDL(1) formation occurs during LCAT-mediated HDL(3)/
HDL(2) interconversion in vitro.-Schmitz, G., and G. Assmann. Isolation of human serum
HDL(1) by
zonal ultracentrifugation.