Apolipoprotein B is a globular protein--morphological studies by electron microscopy.

Water-soluble apolipoprotein B was prepared from fresh plasma by quick isolation of low density lipoproteins and immediate delipidization under non-oxidative conditions. The denatured protein in 6 M guanidine X HCl was reduced and carboxymethylated, dialyzed through 6 M urea/preservatives and to 1% ammonium acetate/0.05% EDTA/0.13% epsilon-amino caproic acid, pH 7.3 under N2 at 4 degrees C. The morphological studies were carried out by electron microscopy with negative staining and freeze fracture. Both these techniques showed that apolipoprotein B is a globular protein with average diameter of 11.48 +/- 1.25 nm (n = 978). The M.W. of apolipoprotein B calculated from this particle size was comparable to that from amino acid sequence.