Fraser D R, Emtage J S
Biochem J. 1976 Dec 15;160(3):671-82. doi: 10.1042/bj1600671.
The chemical identity of vitamin D in the egg of the domestic fowl was studied by analysing radioactivity in eggs from hens injected with [3H]cholecalciferol. Labelled molecules were found throughout the egg, but the concentration of total radioactivity in albumin was only 5-7% of that in yolk. In lipid extracts of yolk, more than 90% of the radioactivity was as unchanged cholecalciferol and 5% as 25-hydroxycholecalciferol. Only about 3% of the radioactivity in albumin was chloroform-soluble, and of this 40% was 25-hydroxycholecalciferol and 15% was cholecalciferol. Evidence is presented to support the idea that the specific transport of cholecalciferol into yolk is mediated by a cholecalciferol-binding protein in blood. This protein forms a complex with yolk proteins in transit from liver to ovary via the blood. A cholecalciferol-binding protein, chromatographically similar to that from blood, was found in egg yolk. It is postulated that cholecalciferol forms part of a complex with its specific binding protein, Ca2+ and the yolk phosphoprotein, phosvitin. This complex is then incorporated into yolk by the thecal cells of the ovarian follicle.
通过分析注射了[3H]胆钙化醇的母鸡所产鸡蛋中的放射性，研究了家鸡鸡蛋中维生素D的化学特性。在整个鸡蛋中都发现了标记分子，但白蛋白中总放射性的浓度仅为蛋黄中的5-7%。在蛋黄的脂质提取物中，超过90%的放射性为未变化的胆钙化醇，5%为25-羟基胆钙化醇。白蛋白中只有约3%的放射性可溶于氯仿，其中40%为25-羟基胆钙化醇，15%为胆钙化醇。有证据支持胆钙化醇特异性转运至蛋黄是由血液中的胆钙化醇结合蛋白介导的这一观点。该蛋白在从肝脏经血液转运至卵巢的过程中与蛋黄蛋白形成复合物。在蛋黄中发现了一种色谱性质与血液中相似的胆钙化醇结合蛋白。据推测，胆钙化醇与其特异性结合蛋白、Ca2+和蛋黄磷蛋白卵黄高磷蛋白形成复合物的一部分。然后该复合物被卵巢卵泡的膜细胞整合到蛋黄中。
