Baldwin D A, Marques H M, Pratt J M
J Inorg Biochem. 1986 Aug;27(4):245-54. doi: 10.1016/0162-0134(86)80065-4.
Titration of the monomeric heme octapeptide from horse heart cytochrome c, microperoxidase-8 (MP-8) from pH 1 to pH 13 in 20% (v/v) methanol-water solutions, mu = 0.1, at 25 degrees C shows three reversible concentration-independent pKs (4.43 +/- 0.09; 8.90 +/- 0.03; 10.48 +/- 0.09) which are ascribed to successive proton loss from the conjugate acid of His (and its coordination to Fe(III)), bound H2O, and from bound His to form an imidazolate complex, respectively. The equilibrium constant for coordination of imidazole between pH 5.5 and 7.0 is independent of pH (logK = 4.45) which proves that His-18 is coordinated to Fe(III) in aqueous solution.
在25℃、离子强度μ = 0.1的20%（v/v）甲醇 - 水溶液中，对来自马心脏细胞色素c的单体血红素八肽（微过氧化物酶 - 8，MP - 8）进行从pH 1至pH 13的滴定，结果显示有三个可逆的与浓度无关的pK值（4.43 ± 0.09；8.90 ± 0.03；10.48 ± 0.09），它们分别归因于His共轭酸（及其与Fe(III)的配位）、结合水以及结合的His上的质子依次丢失，以形成咪唑盐配合物。在pH 5.5至7.0之间咪唑配位的平衡常数与pH无关（logK = 4.45），这证明His - 18在水溶液中与Fe(III)配位。
