ELECTROSTATICS OF HEMOGLOBINS FROM MEASUREMENTS OF THE ELECTRIC DICHROISM AND COMPUTER-SIMULATIONS
ELECTROSTATICS OF HEMOGLOBINS FROM MEASUREMENTS OF THE ELECTRIC DICHROISM AND COMPUTER-SIMULATIONS
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DOI：
10.1016/s0006-3495(95)80226-2
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发表时间：
1995-02-01
影响因子：
3.4
通讯作者：
PORSCHKE, D
中科院分区：
文献类型：
--
作者：
ANTOSIEWICZ, J;PORSCHKE, D
从正常人细胞，镰状细胞，和马血红蛋白进行了研究，在其氧和脱氧形式的电光方法。作为电场强度的函数测量的减少的线性二向色性证明了在250-400德拜单位范围内的永久偶极矩的存在。降低的极限二色性相对较小（小于或等于0.1）;它对镰状细胞的血红蛋白呈阴性，对正常人细胞和马的血红蛋白呈阳性。二色性衰减时间常数在约55至90 ns的范围内。根据各种复杂性的模型，从现有的晶体结构的电光数据的计算，包括质子波动的Monte Carlo模拟与能量评估的有限差分泊松-玻尔兹曼程序。实验的偶极矩与计算结果一致。在人脱氧血红蛋白的情况下，均方根偶极子比平均偶极子高约4.5倍，表明由于质子波动的相对贡献特别大。对于其他血红蛋白分子，均方根偶极与平均偶极的比率小得多（类似于1.1至类似于1.5）。计算表明，二色性衰减时间常数不是简单地由蛋白质的大小/形状决定的，而是受到偶极矢量相对于最大吸光度轴的取向的强烈影响。实验和计算的电光数据的比较提供了一个有用的测试静电计算的准确性和/或晶体和溶液中的结构的等效性。
Hemoglobins from normal human cells, from sickle cells, and from horse were investigated by electrooptical methods in their oxy and deoxy forms. The reduced linear dichroism measured as a function of the electric field strength demonstrates the existence of permanent dipole moments in the range of 250-400 Debye units. The reduced limiting dichroism is relatively small (less than or equal to 0.1); it is negative for hemoglobin from sickle cells and positive for the hemoglobins from normal human cells and from horse. The dichroism decay time constants are in the range from about 55 to 90 ns. Calculations of the electrooptical data from available crystal structures are given according to model of various complexity, including Monte Carlo simulations of proton fluctuations with energies evaluated by a finite difference Poisson-Boltzmann procedure. The experimental dipole moments are shown to be consistent with the results of the calculations. In the case of human deoxyhemoglobin, the root mean square dipole is higher than the mean dipole by a factor of about 4.5, indicating a particularly large relative contribution due to proton fluctuations. The ratio of the root mean square dipole to the mean dipole is much smaller (similar to 1.1 to similar to 1.5) for the other hemoglobin molecules. The calculations demonstrate that the dichroism decay time constants are not simply determined by the size/shape of the proteins, but are strongly influenced by the orientation of the dipole vector with respect to the axis of maximal absorbance. The comparison of experimental and calculated electrooptical data provides a useful test for the accuracy of electrostatic calculations and/or for the equivalence of structures in crystals and in solutions.