Williams R J, Wright P E, Mazza G, Ricard J R
Biochim Biophys Acta. 1975 Nov 18;412(1):127-47. doi: 10.1016/0005-2795(75)90346-3.
Proton NMR spectra at 270 MHz have been measured for horseradish peroxidase and turnip peroxidase isoenzymes (P1, P2, P3 and P7) in both their high spin ferric native states and as the low spin ferric cyanide complexes. Resonances of amino acids near the heme have been identified and used to investigate variations in the structure of the heme crevice amongst the enzymes. Ligand proton resonances have been resolved in spectra of the cyanide complexes of the peroxidases and these provide information on the heme electronic structure. The electronic structure of the heme and the tertiary structure of the heme crevice are essentially the same in the acidic turnip isoenzymes, P1, P2 and, to a lesser extent, P3 but differ in the basic turnip enzyme, P7. The heme electronic structure and nature of the iron ligands in peroxidases are discussed. Further evidence is presented for histidine as the proximal ligand. A heme-linked ionizable group with a pK of 6.5 has been detected by NMR in the cyanide complex of horseradish peroxidase.
已在270兆赫下测量了辣根过氧化物酶和萝卜过氧化物酶同工酶（P1、P2、P3和P7）处于高自旋铁原生状态以及低自旋铁氰化物配合物状态时的质子核磁共振谱。已鉴定出血红素附近氨基酸的共振峰，并用于研究这些酶之间血红素裂隙结构的变化。在过氧化物酶的氰化物配合物谱中已分辨出配体质子共振峰，这些共振峰提供了有关血红素电子结构的信息。在酸性萝卜同工酶P1、P2以及程度稍低的P3中，血红素的电子结构和血红素裂隙的三级结构基本相同，但在碱性萝卜酶P7中则有所不同。讨论了过氧化物酶中血红素的电子结构和铁配体的性质。提出了进一步的证据证明组氨酸是近端配体。通过核磁共振在辣根过氧化物酶的氰化物配合物中检测到一个pK为6.5的血红素连接的可电离基团。
