The Role of Apolipoprotein E in Modulating the Metabolism of Apolipoprotein B-48 and Apolipoprotein B-100 Containing Lipoproteins in Humans
ApoE* is a glycoprotein of 299 amino acids which is associated primarily with VLDL and HDL in human plasma (1,2). It is a polymorphic protein with three common alleles inherited in a co-dominant fashion (3,4), the most common allele coding for apoE3. Homozygosity for this allele is present in approximately 60% of normal subjects, and this is considered to be the normal phenotype (5). Two other common alleles, which code for apoE2 and apoE4, differ from apoE3 by only one amino acid each (6). The allelic frequency of each of these two alleles is approximately 10–15%. Homozygosity for the apoE2 allele is associated with type III hyperlipoproteinemia (3,4) while apoE4 is associated with type V hyperlipoproteinemia (7). Previous investigations have demonstrated that apoE2 is catabolized abnormally slowly in vivo (8) and has a reduced binding affinity for cellular receptors (9). ApoE4 has a normal cellular receptor binding activity when compared to apoE3 (9). The results of these and other studies have led to the proposal that apoE has a major role in modulating the catabolism of remnants of triglyceride-rich lipoprotein particles from the intestine.
KeywordsHomozygous Familial Hypercholesterolemia Fractional Catabolic Rate Remnant Particle Iodine Monochloride VLDL Remnant
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