The Interaction of Apolipoprotein-Alanine (ApoC-III) with Lipids: Study of Structural Features Required for Binding

Abstract

The plasma very low density lipoproteins (VLDL) are the major vehicle for the transport in human blood of endogenously synthesized triglycerides. VLDL particles contain about 50% triglyceride, 20% cholesterol, 20% phospholipid, and 10% protein, by weight (1). The plasma of subjects with Type IV or V hyperlipoproteinemia (2) is rich in VLDL and is a convenient source of these lipoproteins. After the delipidation of VLDL with mixed organic solvents such as chloroform-methanol (2:1) or diethyl ether-ethanol (3:1), the resulting lipid-free apoproteins can be separated on Sephadex G-150 into two major fractions (3). The protein(s) that elutes at the void volume is identical in many respects to the major apoprotein(s) of LDL (4). The other fraction, which is not excluded from the gel, contains a mixture of several apoproteins which can be fractionated on DEAE-cellulose (Figure 1) and have been referred to collectively as the C-proteins (5), the D-peptides (6) or Fraction V (7a). One of these apoproteins, apoLP-Ala (apoC-III), has been studied extensively. It exists as a linear polypeptide containing 79 amino acids (Figure 2) and has a calculated molecular weight of 8751, excluding carbohydrate (8, 9).

Established Investigators of the American Heart Association.