Journal of Lipid Research, Vol 23, 371-379, Copyright © 1982 by Lipid Research, Inc.
Physicochemical characterization of ten fractions of bovine alpha lipoproteins
DL Puppione, ST Kunitake, ML Toomey, E Loh and VN Schumaker
With the onset of milk production, serum concentrations of alpha
lipoproteins in the dairy cow steadily increase, frequently attaining
values greater than 1.5 g/dl. Since these lipoproteins comprise a highly
polydisperse system, we have carried out studies to explore differences
among bovine alpha lipoproteins in the density interval between 1.05 to
1.21 g/ml. Separation into ten fractions was achieved ultracentrifugally in
an isopycnic gradient. Agarose gel electrophoresis showed that all but the
bottom fraction contained alpha lipoproteins as either the major or sole
lipoprotein class. Compositional analyses revealed an increasing percentage
of both protein and phospholipid and a decreasing percentage of cholesterol
with increasing fraction density. The esterified to unesterified
cholesterol ratio ranged from 3 to 8 from the top to the bottom of the
gradient. The densities of the particles obtained from the various
fractions were calculated both from sedimentation velocity measurements and
from compositional analyses. The resulting density values agreed well with
the solution densities of these isopycnic gradient fractions. The major
apoprotein of each fraction was apoA-I. Combining diffusion coefficient
data obtained by intensity fluctuation spectroscopy with sedimentation
velocity data, we were able to calculate molecular weights, frictional
ratios, and Einstein-Stokes radii for three of the fractions. Results are
discussed in terms of previously published data on bovine lipoproteins as
well as other mammalian data.
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