Wilson M T, Ranson R J, Masiakowski P, Czarnecka E, Brunori M
Eur J Biochem. 1977 Jul 1;77(1):193-9. doi: 10.1111/j.1432-1033.1977.tb11657.x.
The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperature-jump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the feric iron while the second and third arise from the binding of the two available amino groups present (the alpha-NH2 of valine and the epsilon-NH2 of lysine). Molecular models indicate that steric retraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide. Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 X 10(6) M-1 s-1 for the intrinsic combination constant of CN- anion with the haem. A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.
通过胃蛋白酶消化从马细胞色素c衍生而来的血红素十一肽的三价铁形式，经历至少三个由pH值诱导的转变，其pK值分别为3.4、5.8和7.6。温度跃升实验表明，其中第一个转变是由于去质子化的咪唑基团与三价铁结合，而第二个和第三个转变则源于存在的两个可用氨基（缬氨酸的α-NH2和赖氨酸的ε-NH2）的结合。分子模型表明，肽上的空间限制决定了这些氨基只能通过分子间键与铁原子配位，从而导致肽的聚合。氰化物结合研究与这些结论一致，并且还得出CN-阴离子与血红素的固有结合常数为3.6×10(6) M-1 s-1。提出了一个描述三价铁十一肽pH依赖性性质的模型。
