Browett W R, Gasyna Z, Stillman M J
Biochem Biophys Res Commun. 1983 Apr 29;112(2):515-20. doi: 10.1016/0006-291x(83)91495-x.
The magnetic circular dichroism spectrum of the compound I species of horseradish peroxidase, which contains an iron (IV) porphyrin pi-cation radical complex, has been measured between 273 K and 4.2 K. The spectrum is temperature independent between 273 K and 30 K. However, very strong temperature dependence is observed below 30 K. These data do not appear to fit the temperature dependence expected for the presence of a simple MCD C term, or combination of C terms, but suggest that an increase in the coupling between the S = 1 iron (IV), and the S = 1/2 porphyrin pi-cation radical occurs forming a degenerate ground state. This increase in coupling below 30 K may be the result of a phase change in the protein which in turn affects the electronic structure of the heme group.
已在273 K至4.2 K之间测量了辣根过氧化物酶化合物I物种的磁圆二色光谱，该物种包含铁（IV）卟啉π-阳离子自由基络合物。该光谱在273 K至30 K之间与温度无关。然而，在30 K以下观察到非常强的温度依赖性。这些数据似乎不符合简单MCD C项或C项组合存在时预期的温度依赖性，但表明S = 1的铁（IV）与S = 1/2的卟啉π-阳离子自由基之间的耦合增加，形成了简并基态。30 K以下这种耦合的增加可能是蛋白质相变的结果，而相变反过来又影响了血红素基团的电子结构。
