Henkens R W, Turner S R
J Biol Chem. 1979 Sep 10;254(17):8110-2.
The three-dimensional conformation of ferricytochrome c results from specific folding of the polypeptide chain around the covalently bound heme so that His-18 and Met-80 are axially coordinated to the Fe(III). The Fe(III)-free, porphyrin protein has an intrinsic viscosity, sedimentation coefficient, and circular dichroism indicative of a compact, globular protein conformation comparable to the holoprotein. Both the porphyrin protein and ferricytochrome c are reversibly denatured by guanidinium chloride. Refolding of the porphyrin protein occurs in essentially a single, exceptionally rapid kinetic phase (tau = 14 ms, 0.75 M guanidinium chloride, pH 6.5, 25 degrees C); whereas refolding of ferricytochrome c occurs in two slower kinetic phases (TAU 1 = 0.10 S, TAU 2 = 20 S) UNDER COMPARABLE CONDITIONS. The presence of Fe(III) in the metalloporphyrin of ferricytochrome c thus has a major effect on the protein folding kinetics. The slow kinetic phase is evidently due to this effect of Fe(III) and not to the slow cis-trans isomerism of the peptide bond of proline residues as has been suggested.
高铁细胞色素c的三维构象源于多肽链围绕共价结合的血红素的特定折叠，使得His-18和Met-80与Fe(III)轴向配位。无铁的卟啉蛋白具有的特性粘度、沉降系数和圆二色性表明其具有与全蛋白相当的紧密球状蛋白构象。卟啉蛋白和高铁细胞色素c都可被氯化胍可逆地变性。卟啉蛋白的复性基本上在一个单一的、异常快速的动力学阶段发生（τ = 14毫秒，0.75 M氯化胍，pH 6.5，25℃）；而在可比条件下，高铁细胞色素c的复性发生在两个较慢的动力学阶段（TAU 1 = 0.10秒，TAU 2 = 20秒）。因此，高铁细胞色素c的金属卟啉中Fe(III)的存在对蛋白质折叠动力学有重大影响。缓慢的动力学阶段显然是由于Fe(III)的这种作用，而不是如有人所提出的脯氨酸残基肽键的缓慢顺反异构化。
