The Structure of Human‐Plasma Low‐Density Lipoprotein B

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Abstract
The X‐ray small‐angle scattering of human plasma lipoprotein B of the low‐density fraction (ϱ= 1.016−1.060 g · cm−3) has been recorded to high precision at different electron density contrasts. The overall structure of the particles is characterized by a quasi‐spherical shape and radial symmetry. A maximum diameter of 23 nm and a molecular weight of 2.4 × 106 have been determined. The internal structure is described in terms of a model consisting of spherical layers with different electron densities indicating that the neutral lipids are arranged in the core of the molecule up to a radius of about 8 nm surrounded by a monolayer of free cholesterol, phospholipids and protein. The neutral lipids are shown to be in an ordered, liquid crystalline state at 4°C and to undergo a thermotropic transition into a disordered state at higher temperatures.