During vitellogenesis the transport of yolk precursor proteins, the vitellogenins (VTG), from the hemolymph into the oocyte is achieved by receptor-mediated endocytosis. Recently the receptor for the VTG of Locusfa migratoria has been isolated. Now a new protocol has been developed for the purification of the VTC receptor of this locust from ovarian membranes. By CHAPS solubilization of the membranes followed by ion exchange and immunoaffinity chromatography, a 1 00-fold purification of the VTG receptor was achieved. The amino acid composition of the receptor protein has been determined. However, first attempts to sequence the receptor failed due to the N-terminal blocking of the molecule. With the same methods the VTG receptor of another locust, Schistocerca gregaria, has been isolated, purified, and characterized. This receptor has an apparent M, of 186 kDa under nonreducing conditions. It recognizes L. migratoria VTG and vice versa. However, in cross-competition experiments in which the Schistocerca VTG competed with Locusfa VTC for binding to the Locusfa VTG receptor, the Schistocerca VTG was less efficient.
Furthermore, the VTG receptor proteins of S. gregaria and L. migraforia are immunologically related as revealed by Western blotting with anti-Locusta VTG receptor antibodies. It appears that important structural elements required for efficient and specific endocytosis of VTG have been conserved.