The polymorphism of apolipoprotein E (apo E) accounts for a substantial amount of the genetic variance of cholesterol levels In man. The e-2 allele lowers and the e-4 allele raises plasma and low density llpoproteln cholesterol levels as compared to the e-3 allele. Whereas the lower cholesterol levels in carriers of the e-2 allele can, at least In part, be attributed to the grossly deficient binding of apo E-2 to the apo B,E receptor, apo E-3 and E-4 bind to the same degree. We used gel filtration and uttracentrlfugatlon to separate lipoproteins and subsequent Immunoblottlng analysis to study the apo E Isoform distribution. We always found lipoproteins of lower density relatively enriched in apo E-4 and high density lipoproteins relatively depleted of apo E-4 as compared to apo E-3. This was also seen In plasma of heterozygous subjects that simultaneously express two apo E Isoforms. Also, the apo E-A-ll complex was directly shown by Immunoblottlng. Furthermore, when purified lodlnated apo E was incubated with plasma In vitro, apo E-4 also reassociated more with lipoproteins of lower density than apo E-3. We conclude that apo E-3 and apo E-4 have a different llpoprotein particle distribution in vivo. This differential llpoproteln distribution may account for differences In the metabolism between apo E-3 and E-4. (Arteriosclerosis 9:405-411, May/June, 1989)

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On isoelectric focusing of human plasma and subsequent immunoblotting, using antii-human serum amyloid A (SAA) antibodies, a genetic variant of SAA was detected in a family of Turkish origin. All affected members of the family were apparent heterozygotes for the mutant protein, which underwent a charge shift of about one charge unit toward the anode. The variant is likely to be a mutant of the most prominent forms of SAA (SAA1 and SAA2, or SAA1 and SAA1 des Arg). The appearance of a genetic variant of two of the six reported SAA-isoforms in human plasma supports the concept of SAA proteins being products of different genes.

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