CHARACTERIZATION OF THE JAPANESE-QUAIL OOCYTE RECEPTOR FOR VERY-LOW-DENSITY LIPOPROTEIN AND VITELLOGENIN

The plasma membrane receptor for VLDL and vitellogenin from oocytes of Japanese quail compared with that of another domestic fowl, the chick en (Gallus domesticus). When visualized by ligand blotting with biotin ylated or I-125-labeled lipoproteins, the quail VLDL/vitellogenin rece ptor had an apparent M(r) of 95 kDa under nonreducing conditions, iden tical to that of the chicken receptor. Upon analysis by ligand blottin g, binding of radiolabeled quail plasma VLDL to the quail oocyte recep tor seemed to be saturable and exhibited high affinity (apparent K-d o f 13.9 mg/L). Cross-reactivity, at the level of ligand recognition, wa s observed between quail and chicken VLDL/vitellogenin receptors, and immunological relatedness was demonstrated by Western blotting with a rabbit anti-chicken oocyte VLDL receptor antibody. In contrast, a spec ies difference was observed in the apolipoprotein VLDL-II moiety of pl asma VLDL. Chicken apolipoprotein VLDL-II, an 82-amino acid protein wi th a disulfide crosslink at residue 75 (the sole cysteine residue), ex isted as a homodimer of 9.5 kDa subunits and, to a lesser extent, as a monomer. Quail apolipoprotein VLDL-II existed only in monomeric form without reduction and lacked cysteine. The present results demonstrate that, despite a difference in an apolipoprotein moiety of VLDL, quail and chicken oocyte lipoprotein receptors share key structural and fun ctional elements. This lends further support to the notion that recept or recognition is mediated by the common VLDL component, apolipoprotei n B.