アメマスSalvelinus leucomaenisビテロゲニンの卵黄蛋白質への特異的分解 Specific Proteolysis of Vitellogenin to Egg Yolk Proteins in White Spotted-charr Salvelinus leucomaenis
Vitellogenin (Vg) was purified from white spotted-charr <i>Salvelinus leucomaenis</i> serum and biotinylated (b-Vg). The b-Vg was digested under mild acidic conditions by bovine cathepsin-D (BCD) or a water soluble fraction of charr eggs (WSF), Digests were analyzed by 5.0-22.5% gradient SDS-polyacrylamide gel electrophoresis (SDS-PAGE), Westem blotting, and gel filtration on Superose 6. Westem blotting was done using: 1) streptavidin coupled to horseradish peroxidase (HRPO) to identify biotinylated products of b-Vg digestion, and 2) antisera against lipovitellin (a-Lv) or β-component (a-β') to immunologically relate digestion products to specific charr egg yolk proteins. With respect to antigenicity and apparent molecular weight, fragments resulting from digestion of b-Vg by WSF or BCD were almost indistinguishable from those found in charr egg yolk, except for phosvitin (Pv). Pv-related phosphorus in BCD digests eluted at a position corresponding to a molecular weight slightly greater than that of Pv in egg yolk. The present study is the first to demonstrate <i>in vitro</i> conversion of salmonid Vg to its related egg yolk proteins. The similar catalytic effect of WSF or BCD on <i>in vitro</i> generation of egg yolk proteins suggests that cathepsin-D, present in WSF or intact eggs, may play a key role in natural yolk formation in salmonids.
日本水産学会誌 63(5), 701-708, 1997-09-15