Urnes P
J Gen Physiol. 1965 Sep;49(1):Suppl:75-103. doi: 10.1085/jgp.49.1.75.
The central question to be discussed in this paper is whether the structure established for sperm whale myoglobin in the crystalline state is the same as that of the protein in solution. As judged by its ultraviolet optical rotatory dispersion, the helical content of metmyoglobin in solution does not differ from that in the crystal, 77 per cent. Although an uncertainty of about +/-5 per cent must attach to this result, it excludes many alternative arrangements of the polypeptide chain. The folding of the chain may be further restricted to the basic form seen in the crystal if the dimensions of the molecule in solution and the interactions of specific chemical groups are taken into account. Since the rotatory dispersion of metmyoglobin is constant with respect to ionic strength, and since the dispersions of reduced and oxymyoglobin reveal no change in helical content upon their formation from metmyoglobin, one may infer that the structure of the protein is largely maintained both as it dissolves and during its reversible combination with oxygen. The crystallographic model of myoglobin thus offers a structural basis for attempting to explain its physiological function in solution. The relevance of this conclusion to the crystal-solution problems presented by other species of protein is then best seen in the light of common factors that govern the equilibrium of all proteins between crystal and solution.
本文要讨论的核心问题是，结晶态的抹香鲸肌红蛋白所确立的结构是否与溶液中的蛋白质结构相同。根据其紫外旋光色散判断，溶液中高铁肌红蛋白的螺旋含量与晶体中的并无差异，均为77%。尽管该结果必然存在约±5%的不确定性，但它排除了多肽链的许多其他排列方式。如果考虑溶液中分子的尺寸以及特定化学基团的相互作用，链的折叠可能会进一步局限于晶体中所见的基本形式。由于高铁肌红蛋白的旋光色散相对于离子强度是恒定的，并且由于还原型和氧合肌红蛋白在由高铁肌红蛋白形成时其旋光色散并未显示螺旋含量的变化，因此可以推断，蛋白质的结构在溶解过程中以及与氧的可逆结合过程中基本保持不变。因此，肌红蛋白的晶体学模型为尝试解释其在溶液中的生理功能提供了结构基础。然后，根据控制所有蛋白质在晶体和溶液之间平衡的共同因素，最好地理解这一结论与其他蛋白质种类所呈现的晶体 - 溶液问题的相关性。
