Phylogenetic distribution of apolipoproteins A-I and E in vertebrates as determined by Western blot analysis.

A putative apolipoprotein E (apoE) has been identified in the HDL and VHDL fractions of the turtle. This observation is of particular interest considering apoE has been reported absent in the domestic hen (Hermier et al., '95; Biochim Biophys Acta: 105-118, 1995) and thus presumed absent in nonmammalian vertebrates altogether. As a result, partial amino acid sequencing of this protein was performed and revealed that one fragment shared 41% sequence identity to human apoE. Western blot analysis using antisera to apoE demonstrated cross-reactivity to a 34-kDa protein (putative apoE) in turtle plasma. Further investigation using anti-apoE antibody in Western blot analysis detected immunoreactive apoE in the plasma of lamprey, spiny dogfish, skate, and alligator, but not in flounder, newt or python; its absence in several species of birds was confirmed. Using anti-apoA-I antibody, apoA-I was detected in all vertebrate groups except a representative teleost (flounder). Apo-A-I antibody cross-reacted weakly with some putative apoE proteins (chicken, spiny dogfish and skate) and the reverse was true for anti-apoE, which cross-reacted with putative apoA-I in birds, reptiles, and elasmobranchs, confirming the molecular similarity and phylogenetic relatedness of these two proteins.