Electrostatic effect on electron transfer between cytochrome b5 and cytochrome c

The binding and electron transfer between wild type, E44A, E56A, E44/56A, E44/48/56A/D60Aand F35Y variants of cytochrome b5 and cytochrome c were studied. When mixed with cytochrome c, the cytochrome b5E44/48/56A/D60A did not show the typical UV-vis difference spectrum of absorption, indicating that the alteration ofthe surface electrostatic potential obviously influenced the spectrum. The electron transfer rates of wild type cytochromeb5, its variants and cytochrome e at different temperature and ionic strength exhibited an order of F35Y > wild type >E56A > E44A > E44/48/56A/D60A. The enthalpy and entropy of the reaction did not change obviously, suggestingthat the mutation did not significantly disturb the electron transfer conformation. The investigation of electron transfer rateconstants at different ionic strength demonstrated that electrostatic interaction obviously affected the electron transfer pro-cess. The significant difference of Cyt b5 F35Y and E44/48/56A/D60A from the wild type protein further confirmed thegreat importance of the electrostatic interaction in the protein electron transfer.     

Roles of Phe58 residue in stabilizing structure of cytochrome b<Subscript>5</Subscript>

To understand effect of π-stacking interactions between the side chain of aromatic amino acids and the porphyrin ring on structures and properties in cytochrome b₅ (cyt b₅), the Phe58 residue was mutated to tyrosine and tryptophan, respectively by site-directed mutagenesis. The denaturation of cyt b₅ F58W and F58Y toward guanidine hydrochloride was examined by UV-visible and fluorescence spectroscopy. The kinetics of heme transfer reactions between apo-myoglobin and the mutants were studied. The results indicated that the mutation of F58 residue for Y58 or W58 reduced the interaction between of peptide and the heme group, resulting in decrease of the T _m and C _m values of the proteins, increase of the heme transfer reaction rate, and shifts of the redox potential.     

铀酰离子-细胞色素b_5复合物的分子动力学模拟

铀酰离子(UO_2~(2+))的生物学毒性是由于它能与蛋白质形成稳定的复合物而破坏了蛋白的正常功能。通过使用分子建模和分子动力学(molecular dynamics,MD)模拟,对铀酰离子-细胞色素b_5复合物(UO_2~(2+)-cyt b_5)进行了结构预测。模拟结构显示,UO_2~(2+)通过配位和氢键作用结合到Cyt b_5中谷氨酸Glu37和Glu43,导致Cyt b_5的动力学行为发生轻微改变,而对蛋白整体结构几乎不产生影响。这些现象与Cyt b_5的体内形成以及作为电子传递蛋白的生物功能紧密相联。这些原子水平上理论信息的获得,为铀酰离子的毒性机制,尤其是涉及Cyt b_5的细胞凋亡,提供了深刻内涵。     

Expression, purification and characterization of the soluble CuA domain of cytochrome c oxidase ofParacoccus versutus

The key subunit Ⅱ of cytochrome c oxidase (CcO) contains a soluble binuclear copper center (Cu_A) domain. The Cu_A domain of Paracoccus versutus was cloned, expressed, purified and characterized. The gene encoding the Cu_A domain in pET11d vector was expressed in E. coli BL21 (DE3). The results showed that the Cu_A domain was expressed mostly in inclusion bodies and the Cu_A domain protein synthesized in E. coli cells represents approximately 10 percent of the total cellular proteins. Dissolved in urea, dialyzed and recombined with Cu⁺/Cu²⁺ and purified by the Q-sepharose fast flow anion-exchange column and Sephadex G-75 gel filtration column, the soluble purple-colored protein, which shows a single band in electrophoresis, was obtained. The UV-visible absorption spectrum of Cu_A domain showed that there are intense band at 478 nm and a shoulder peak at 530 nm, and two weak bands at 360 and 806 nm respectively, which can be assigned to the charge transfer and the interactions of obitals of Cu—S and Cu——Cu in the mixed-valence binuclear metal center (Cu₂S₂R₂). The far-UV CD spectrum indicated that this domain is predominantly in β-sheet structure. The fluorescence spectra showed that its maximal excitation wavelength and maximal emission wavelength are at 280 and 345 nm, respectively.     

Nb_2O_5/CdS纳米粒子的制备及其光催化性能研究

通过简单的沉淀法合成了Nb2O5/Cd S纳米粒子,利用XRD、TEM、XPS对其进行了表征,采用制备的Nb2O5/Cd S纳米粒子在可见光照射下对罗丹明B进行了降解实验.结果表明:负载在Nb2O5表面上的Cd S粒径大小较均一,约为35 nm,在可见光照射下,Cd S质量比为20%的Nb2O5/Cd S纳米粒子光催化活性最佳,可见光照射下3 h对罗丹明B降解率为98%,经过3次循环利用,发现其具有良好的光催化稳定性.     

Preparation and luminescence characteristics of Sr3SiO5：Eu^2＋ phosphor for white LED

The Sr3SiO5：Eu^2＋ phosphor was synthesized by high temperature solid-state reaction. The emission spectrum of Sr3SiO5：Eu^2＋ shows two bands centered at 487 and 575 nm, which well agree with the theoretic values of emission spectrum. The excitation spectrum for 575 nm emission center has several excitation bands at 365, 418, 458 and 473 nm. And the results show that the emission spectrum of Sr3SiO5：Eu^2＋ is influenced by the Eu^2＋ concentration. The relative emission spectra of the white-emitting InGaN-based YAG：Ce^3＋ LED and Sr3SiO5：Eu^2＋ LED were investigated. The results show that the color development of InGaN-based Sr3SiO5：Eu^2＋ is better than that of InGaN-based YAG：Ce^3＋, and the CIE chromaticity of InGaN-based Sr3SiO5：Eu^2＋ is （x=0.348, y=0.326）.