Huggins L G, Waite J H
Marine Biology/Biochemistry Program, College of Marine Studies, University of Delaware, Lewes 19958.
J Exp Zool. 1993 Apr 1;265(5):549-57. doi: 10.1002/jez.1402650511.
The marine triclad Bdelloura candida (Turbellaria) episodically deposits stalked eggshells onto the gill lamellae of the horseshoe crab Limulus polyphemus. Ultrastructural and biochemical analyses indicate that the eggshells consist of primary inner and secondary outer layers. Protein of the primary layer is rich in glycine, aspartate/asparagine, serine, and 3,4-dihydroxyphenylalanine (Dopa). In this regard it resembles the eggshell compositions of other members of the phylum Platyhelminthes. The primary layer appears to be derived from precursors produced in the vitelline cells of the flatworm. Each egg-laying episode consumes all of the precursor-containing vitelline cells. A Dopa-containing protein, vitelline protein 1 (Vp1), has been isolated from B. candida and resembles the primary eggshell layer in its composition. Vp1 has an apparent molecular weight of 34.4 and an acidic pI. Dopa-containing proteins are presumed to be directly involved in the cross-linking reactions that accompany quinone-tanning. The secondary outer layer of the eggshell may serve to adhere the eggshell to the gill. Its amino acid composition is unlike that of the primary eggshell and nothing is known about its precursors.
海生三肠涡虫白涡虫（Bdelloura candida，涡虫纲）会间歇性地将带柄卵壳沉积在鲎（Limulus polyphemus）的鳃片上。超微结构和生化分析表明，卵壳由内层初级层和外层次级层组成。初级层的蛋白质富含甘氨酸、天冬氨酸/天冬酰胺、丝氨酸和3,4-二羟基苯丙氨酸（多巴）。在这方面，它类似于扁形动物门其他成员的卵壳组成。初级层似乎源自扁形虫卵黄细胞产生的前体。每次产卵过程都会消耗所有含有前体的卵黄细胞。一种含多巴的蛋白质，卵黄蛋白1（Vp1），已从白涡虫中分离出来，其组成与卵壳初级层相似。Vp1的表观分子量为34.4，pI呈酸性。含多巴的蛋白质被认为直接参与了醌鞣制伴随的交联反应。卵壳的次级外层可能用于将卵壳粘附在鳃上。其氨基酸组成与卵壳初级层不同，且对其前体一无所知。
