Determination of relative spin concentration in some high-spin ferric proteins using E/D-distribution in electron paramagnetic resonance simulations.
Determination of relative spin concentration in some high-spin ferric proteins using E/D-distribution in electron paramagnetic resonance simulations.
复制标题
在电子顺磁共振模拟中使用 E/D 分布确定一些高自旋三价铁蛋白的相对自旋浓度。
DOI：
10.1016/s0006-3495(87)83311-8
复制
发表时间：
1987
影响因子：
3.4
通讯作者：
Gaffney,BJ
中科院分区：
文献类型：
--
作者：
Yang,AS;Gaffney,BJ
线形模拟的多个，重叠的X-波段电子顺磁共振（EPR）光谱在两个非血红素，高自旋铁蛋白质：苯丙氨酸羟化酶（PAH）和二铁转铁蛋白。计算的目的是确定EPR可见的每个站点的铁的分数。模拟仅限于在g值大于1.7时发生的实验可获得的跃迁。在PAH和转铁蛋白中，至少一个铁位点的特征在于零场分裂参数E/D的比率接近1/3和宽的不对称线形。在模拟中使用E/D值的分布来解释这种宽度和不对称性。为了检验E/D分布模型，通过模拟拟合了几种盐浓度下二铁转铁蛋白的实验X带光谱。在这个测试中，首先低场功能所产生的最低Kramers的双重能级之间的过渡模拟使用E/D分布的两个网站。第二，参数，提供了一个很好的适合最低的二重态过渡也显示，以配合共振附近的有效g值为4.3，从中间的克莱默斯二重态过渡。当应用于PAH在静止状态下的光谱，E/D-分布的方法占的强度的两个主要物种的铁。另一种的特征在于E/D = 0.032，并且可以使用频率扫描的高斯线形来模拟静息酶的该部分的光谱。还模拟了处于底物饱和状态的酶的光谱。模拟结果与以前的生化研究一致，表明只有E/D = 0.032的铁形式参与催化。
Lineshape simulations are presented for the multiple, overlapping X-band electron paramagnetic resonance (EPR) spectra in two non-heme, high-spin iron proteins: phenylalanine hydroxylase (PAH) and diferric transferrin. The aim of the calculations is to determine the fraction of iron contributing to each of the sites visible by EPR. The simulations are limited to the experimentally accessible transitions occurring at g-values greater than 1.7. In both PAH and transferrin, at least one of the iron sites is characterized by the ratio of zero-field splitting parameters, E/D, near 1/3 and a broad, asymmetric lineshape. A distribution in E/D-values is used in the simulations to account for this breadth and asymmetry. To test the E/D-distribution model, experimental X-band spectra of diferric transferrin at several salt concentrations are fit by simulation. In this test, first the low-field features arising from transitions between the lowest Kramers doublet levels are simulated using E/D-distributions for two sites. Second, parameters that provide a good fit for the lowest doublet transitions are shown also to fit the resonance near an effective g-value of 4.3 from the middle Kramers doublet transition. When applied to spectra of PAH in the resting state, the E/D-distribution approach accounts for the intensity of one of the two major species of iron. The other species is characterized by E/D = 0.032, and the spectrum of this portion of the resting enzyme may be simulated using a frequency-swept Gaussian lineshape. Spectra for the enzyme in an inhibitor-saturated state are also simulated. The simulations are consistent with previous biochemical studies that indicate that only the E/D = 0.032 form of iron participates in catalysis.