Purification and properties of vitellogenin and vitellin from a tick,Ornithodoros moubata

Summary The vitellogenin (Vg) and vitellin (Vn) of a soft tick,Ornithodoros moubata, were purified from reproductive female haemolymph and from eggs, respectively. The Vg preparation displayed two components (Vg-1 and Vg-2) on polyacrylamide gel electrophoresis (PAGE), both of which reacted with anti-Vn serum. The Vn and Vg-2 preparations were homogeneous as judged by PAGE, electron microscopy, and immunodiffusion, whereas the Vg-1 always contained a small amount of Vg-2. The electron micrographs of Vn and Vg-2 showed a rugby-ball shape with a cleft at the middle of the molecules, while Vg-1 appeared as half of Vn or Vg-2 in shape and size. This together with the data on molecular weights (600, 000 for Vn and Vg-2, 300, 000 for Vg-1) suggests that the Vn and Vg-2 are dimers of Vg-1. Six polypeptides (P1–P6, mol wt 100, 000–215, 000) for Vgs and six polypeptides (P3–P8, mol wt 50, 000–160, 000) for Vn were demonstrated by SDS PAGE; P3–P6 were common to Vgs and Vn. These observations suggest proteolytic processing from larger to smaller polypeptides. The Vn contained 7.6% lipids with triacylglycerol as the major neutral lipid and 12.4% carbohydrates with mannose as the major sugar. The Vn and Vgs showed a reddish brown coloration due to the presence of haem compound(s). The amino acid composition of Vn was high in glutamic acid, proline, valine and leucine but low in methionine and isoleucine. The isoelectric point of Vn and Vgs was pH 6.9. Unlike Vg and Vn of insects, the Vgs and Vn of tick were soluble in distilled water.Abbreviations Vg vitellogenin - Vn vitellin - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecylsulfate