Herskovits T T, Erhunmwunsee L J, San George R C, Herp A
Biochim Biophys Acta. 1981 Jan 30;667(1):44-58. doi: 10.1016/0005-2795(81)90065-9.
The hemocyanin of the blue crab, Callinectes sapidus has two major components sedimenting with approximate sedimentation coefficients of 17 S and 25 S. Molecular weight data based on light scattering and sedimentation equilibrium measurements at pH 7.8 suggest that the two components have molecular weights of approximately 450 000 and 900 000 in the presence of stabilizing Ca2+. In the absence of Ca2+, the molecular weights are found to be about 5% lower, suggesting some dissociation of the hemocyanin components. Circular dichroism and optical rotatory dispersion measurements in the far-ultraviolet region gave nearly identical spectra for the two components. Based on the reference parameters of Chen et al. (Chen, Y.H., Yang, J.T. and Martinez, H.M. (1972) Biochemistry 11, 4120--4131 and Chen, Y.H., Yang, J.T. and Chan, K.H. (1974) Biochemistry 13, 3340--3359), estimates of 16--20% alpha-helix, 40--60% beta-structure, and 30--40% random organization were obtained for the two hemocyanin components. Exposure to 6 M Gdn HCl gave light scattering molecular weights of approx. 68 000 and 77 000, which is close to one-sixth of the molecular weight of the 17 S component. These results support the view that the two components of C. sapidus hemocyanin share the hexameric and dodecameric organization common to arthropod hemocyanins. The salts of the Hofmeister series and the ureas are found to dissociate the dodecameric component with the former exhibiting the usual order of effectiveness of NaCl, NaBr, NaI, and NaClO4 dissociation, while the ureas show an inverse order of decreasing effectiveness in going from urea to methyl-, ethyl- and propylurea. This suggests that polar and ionic interactions are relatively more important than hydrophobic interactions for the stabilization of the dodecameric form of C. sapidus hemocyanin. The dissociation behavior of the 17 S hexameric species by GdnHCl in the 0--1.5 M concentration region (where essentially no denaturation occurs), based on light scattering molecular-weight measurements, is satisfactorily accounted for by equations describing the dissociation of hexamers to monomers.
青蟹（Callinectes sapidus）的血蓝蛋白有两个主要成分，沉降系数约为17 S和25 S。基于在pH 7.8条件下的光散射和沉降平衡测量得到的分子量数据表明，在有稳定作用的Ca2+存在时，这两个成分的分子量分别约为450 000和900 000。在没有Ca2+的情况下，分子量降低约5%，这表明血蓝蛋白成分有一定程度的解离。在远紫外区域的圆二色性和旋光色散测量显示，这两个成分的光谱几乎相同。根据Chen等人（Chen, Y.H., Yang, J.T. 和 Martinez, H.M. (1972) Biochemistry 11, 4120--4131以及Chen, Y.H., Yang, J.T. 和 Chan, K.H. (1974) Biochemistry 13, 3340--3359）的参考参数，估算出血蓝蛋白的这两个成分含有16 - 20%的α-螺旋、40 - 60%的β-结构和30 - 40%的无规结构。用6 M盐酸胍处理后，光散射测得的分子量约为68 000和77 000，接近17 S成分分子量的六分之一。这些结果支持了这样一种观点，即青蟹血蓝蛋白的两个成分具有节肢动物血蓝蛋白共有的六聚体和十二聚体结构。发现霍夫迈斯特系列盐类和脲类会使十二聚体成分解离，前者表现出通常的NaCl、NaBr、NaI和NaClO4解离效果顺序，而脲类从尿素到甲基脲、乙基脲和丙基脲的解离效果递减顺序则相反。这表明对于青蟹血蓝蛋白十二聚体形式的稳定，极性和离子相互作用相对比疏水相互作用更重要。基于光散射分子量测量，在0 - 1.5 M浓度范围内（基本未发生变性），GdnHCl对17 S六聚体物种的解离行为可以用描述六聚体解离为单体的方程令人满意地解释。
