The structure of vitellogenin. Multiple vitellogenins in Xenopus laevis give rise to multiple forms of the yolk proteins.
1981; Elsevier BV; Volume: 256; Issue: 16 Linguagem: Inglês
10.1016/s0021-9258(19)68890-3
ISSN1083-351X
Autores Tópico(s)Aquaculture disease management and microbiota
ResumoWe describe the purification and characterization of the major vitellogenin-derived yolk polypeptides from the platelets of Xenopus oocytes.Five different types of yolk polypeptides were isolated, three of which (lipovitellin 1, lipovitellin 2, and phosvitin) correspond to previously described yolk proteins.Two new phosphorylated yolk polypeptides, named phosvette 1 and phosvette 2, were also isolated and found to have M, = 19,000 and 13,000-14,000, respectively.While phosvitin had 7.4% protein-phosphorus, phosvette 1 was found to have 4.8% protein-phosphorus and phosvette 2 contained 10.7% protein-phosphorus.Amino acid analyses of phosvette 1 and phosvette 2 showed that these proteins were not derived from the other yolk proteins.Lipovitellin 1 and lipovitellin 2 could each be resolved into three components by sodium dodecyl sulfate-gel electrophoresis, termed the a, /I, and y forms in order of their increasing electrophoretic mobility.Ferguson plot analysis of lipovitellin l a , p, and y yielded M, = 121,000,116,000, and 111,000, respectively.Lipovitellins 2a, p, and y have M, = 34,000, 31,500, and 30,500, respectively.Phosvitin displayed very anomalous behavior during sodium dodecyl sulfate-gel electrophoresis, but dephosphorylated phosvitin demonstrated no anomalous behavior and resolved as two bands of M, = 37,500 and 39,000.Sedimentation equilibrium and gradient gel electrophoresis of native phosvitin yielded values of M, = 33,000 and 34,000, respectively.An analysis of the stoichiometry among the yolk proteins showed that the ratio among the lipovitellins, phosvitin, and the phosvettes was 1:0.69:0.25.We propose that the multiple yolk proteins are products of the cleavage of multiple vitellogenin molecules, and that phosvitin and the phosvettes are alternate cleavage products arising from homologous regions of different parent vitellogenin molecules.Vitellogenin is the sex-limited yolk precursor protein in oviparous vertebrates (1).The hepatic synthesis of this large ( M , -460,000) phospholipoglycoprotein (2) can be induced in
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