ISOLATION AND CHARACTERIZATION OF APOLIPOPHORIN-III FROM THE GIANT WATER BUG (LETHOCERUS-MEDIUS)

Upon injection of synthetic adipokinetic hormone, lipophorin from Lethocerus medius decreased in ensity and became associated with apolipophorin-III (apoLp-III), ApoLp-III isolated from hemolymph of Lethocerus medius had a M(r) = 19,000 and an amino acid composition high in methionine, in comparison with other apoLp-IIIs. Its circular dichroism spectrum was consistent with a protein with secondary structure of predominantly alpha-helix, NH2-terminal sequence alignment with apoLp-III sequences from other species showed a conservation of the hydrophobic or hydrophilic properties of residues at each position rather than of specific amino acids, ApoLp-III from Lethocerus medius has the potential to form amphipathic alpha-helices, similar to those found in the three-dimensional structure of Locusta migratoria apoLp-III. A portion of the apoLp-III molecules that are not associated with lipophorin contained the blue chromophore, biliverdin.