A rapid flat gel isoelectric focusing method has been developed for the determination of VLDL apolipoprotein (apo) E isoform patterns. Isoelectric focusing in 5% polyacrylamide flat gel with 8M urea and 2.8% pharmalyte (PH 4-6.5)(Pharmacia) was carried out at 3000 V and 4° for 1 hr under a constant power of 30 W, using a flat bed apparatus FBE 3000 (Pharmacia) and an electrophoresis constant power supply ECPS 3000/150 (Pharmacia).The separation of apo E isoform bands was good, and isoelectric points were determined 5.95 for apo E4, 5.81 for apo E3 and 5.68 for apo E2 in our focusing system. We analyzed apo E isoform patterns in our population (n=123) using this focusing method.
The results obtained were as follows;
1) The apo E phenotype frequencies were 0.0% for E2/2, 6.5% for E3/2, 71.6% for E3/3, 0.8% for E4/2, 19.5% for E4/3 and 1.6% for E4/4, indicating that Japanese have a higher frequency of ε3 allele and a lower frequency of ε2 allele than either German or Americans.
2) Two phenotypes, apo E3/3 and E3/2 were differentiated on the basis of the apo E2/E3 ratios. The ratio was 0.38±0.02 for group E3/3 and 1.12±0.04 for group E3/2. No overlap was observed between the two groups. The cut-off point between the two groups was assumed to be approximately 0.9 in our focusing system.
This method is useful for the analysis of apo E isoform patterns.
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