Lange R, Hui Bon Hoa G, Debey P, Gunsalus I C
Acta Biol Med Ger. 1979;38(2-3):143-52.
Spin state changes in the iron center of cytochrome P-450 during the catalytic cycle suggest alterations in the heme environment that insure proper substrate binding, an increase in redox potential, the formation of an active Fe-O complex, and the attack on the substrate. We used the spin state changes of the iron following physico-chemical perturbations, as an intrinsic probe of discrete changes around the heme, or of larger ones in the protein conformation. These environmental perturbations included temperature, solvent, substrate, and ionic environment. Aqueous and hydro-organic buffers provide complementary data and interpretations; the mixed solvent accommodates temperatures suitable for direct reaction rate measurements and amplified low to high spin transition. The results suggest that the group determining the heme spin state is influenced by the electrostatic potential created by several negative charges near the heme; the modulation of the spin state by various factors reflects the modulation of the electrostatic potential and of the internal paH value. Conformational changes of the whole protein are also indicated by the large entropy terms and their variation with experimental conditions.
细胞色素P-450铁中心在催化循环过程中的自旋态变化表明，血红素环境发生了改变，以确保底物的正确结合、氧化还原电位的升高、活性Fe-O复合物的形成以及对底物的攻击。我们利用物理化学扰动后铁的自旋态变化，作为血红素周围离散变化或蛋白质构象较大变化的内在探针。这些环境扰动包括温度、溶剂、底物和离子环境。水性和水-有机缓冲液提供了互补的数据和解释；混合溶剂可适应适合直接反应速率测量的温度，并放大低自旋到高自旋的转变。结果表明，决定血红素自旋态的基团受血红素附近几个负电荷产生的静电势影响；各种因素对自旋态的调节反映了静电势和内部pH值的调节。整个蛋白质的构象变化也由大的熵项及其随实验条件的变化所表明。
