PRECURSOR-PRODUCT RELATIONSHIP BETWEEN CHICKEN VITELLOGENIN AND THE YOLK PROTEINS - THE 40-KDA YOLK PLASMA GLYCOPROTEIN IS DERIVED FROM THEC-TERMINAL CYSTEINE-RICH DOMAIN OF VITELLOGENIN-II

Chicken vitellogenin, a serum lipoprotein specific for laying hens, ha s been thought to be proteolytically cleaved into the heavy and light chain lipovitellins and phosvitin, the major yolk granule proteins, du ring or after transportation into oocyte. In this study, another prote olytic product of vitellogenin has newly been isolated from the 'beta- livetin' fraction of yolk plasma. It is a yolk glycoprotein of 40 kDa (YGP40) with asparagine-linked carbohydrate chain(s) recognized by Con canavalin A and castor bean lectin (RCA-I), and it is identified as a C-terminal cysteine-rich fragment of the major vitellogenin (vitelloge nin II), the cysteine-rich domain homologous to D2 region of von Wille brand factor. Another yolk plasma glycoprotein of 42 kDa is suggested to be one of the proteolytic products of the minor vitellogenin (vitel logenin I). Both 30 kDa and 42 kDa glycoproteins were shown to be pres ent in growing oocytes but absent in laying hen's serum. Limited prote olysis of vitellogenin II with cathepsin D produced a 40 kDa protein w ith reactivity to anti-YGP40 antibody. Gel filtration analysis of vite llogenin II digested with cathepsin D showed that YGP40 dissociated fr om lipovitellin-phosvitin complex after the proteolytic cleavage, Thes e results suggest that after incorporation from serum via a specific r eceptor vitellogenin II is cleaved in the oocyte into four fragments, heavy and light chain lipovitellins, phosvitin and YGP40, and that YGP 40 is released into the yolk plasma before or during compartmentation of lipovitellin-phosvitin complex into the yolk granule.