PMID: 6405003Mar 1, 1983Paper

Selective proteolytic digestion as a method for the modification of human HDL3 structure.

Journal of Lipid Research
J B Swaney

Abstract

Trypsin digestion of human high density lipoprotein (d 1.125-1.21 g/ml) on which the lysine residues have been masked with the reversible blocking group, 2,3,4,5-tetrahydrophthallic anhydride (THPA), was found to result in the fragmentation of the apoA-I component, but not the apoA-II component of this lipoprotein particle. Approximately 50-80% of the apoA-I polypeptide was found in a lipid-free fraction, while the residual apoA-I material plus the apoA-II moiety constituted a core particle that contained most of the original lipid. Immunological analysis indicated that such fragmentation did not affect the immunoreactivity of apoA-II, but that all immunoreactivity of apoA-I was lost within the first 30 min of trypsinization. By column chromatography and electron microscopy this core particle appeared identical in size with the untrypsinized THPA-modified HDL(3) material. Size analysis of the core particle peptides suggests that not all of the A-I molecules present on the HDL(3) are trypsinized to the same extent, which indicates possible nonequivalence of these peptide chains. Analysis of the amino acid composition revealed a somewhat greater proportion of hydrophobic residues in the lipid-bound fraction than in the lipid-free...Continue Reading

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