腹足纲Helix pomatia βC-血清蛋白的功能单位d,e和f中一个半胱氨酸-组氨酸之间硫醚桥键的鉴定

对腹足纲软体动物罗曼蜗牛Helix pomatia的氧运输蛋白（βc-血清蛋白）的功能单位d，e和，中的一个半胱氨酸-组氨酸之间的硫醚桥键进行了研究。以该βc-血清蛋白为载体，通过限制性胰蛋白酶水解，产生片段a—c，ef，以及功能单位d，g，和h。以片段ef降解后的产物为研究对象，通过亲合色谱的分离纯化，得到功能单位P和f。通过对羧甲基化功能单位d的胰蛋白酶和链霉蛋白酶水解，得到一个含有硫醚桥键的4肽。同样在吡啶乙基化功能单位e和f的胰蛋白酶水解产物中也分离得到一个含有相同硫醚桥键的小肽。因此一个半胱氨酸-组氨酸之间硫醚桥键的存在似乎是腹足纲软体动物罗曼蜗牛Helix pomatia氧运输蛋白（βc-血清蛋白）功能单位的一个共有的特征。

Identification of A Cysteine-Histidine Thioether Bridge Bond in Functional Units d, e and f of βC-haemocyanin of The Gastropod Helix Pomatia

A thioether bridge between a cysteine and a histidine residue in functional units d, e and f of βC-haemocyanin of the gastropod Helix pomatia was investigated. The limited trypsinolysis on tenth molecules of βC-haemocyanin of Helix pomatia at pH=8.2 yielded the fragments a-c, e f, and the functional units d, g, and h (present as dimers h2 ). The mixture of functional units e and f after limited fragmentation of fragment e f,were further fractionated with an affinity chromatography in the presence of α-methylglucoside, yielded functional units e and f. A tetrapeptide which contained a thioether bridge between cysteine-60 and histidine-62 was obtained after treatment of the carboxymethylated functional unit d with trypsin and pronase. As could be deduced from the analysis of the peptides, strongly absorbing at 255nm and found in the sediments (cores) after trypsinolysis of the pyridylethylated functional units e and f, one of these cysteine residues (cysteine-60 in the numbering of functional unit d) was involved in the formation of a thioether bridge with histidine-62. Thus the presence of a cysteine- histidine thioether bridge seems to be a general feature of functional units from the βC-haemocyanin of the gastropod Helix Pomatia.