Egan T J, Mavuso W W, Ncokazi K K
Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
Biochemistry. 2001 Jan 9;40(1):204-13. doi: 10.1021/bi0013501.
Formation of beta-hematin in acidic acetate solution has been investigated using quantitative infrared spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. The process occurs via rapid precipitation of amorphous (or possibly nanocrystalline) hematin, followed by slow conversion to crystalline beta-hematin. Definitive evidence that the reaction occurs during incubation in acetate medium, rather than during the drying stage, is provided by X-ray diffraction and infrared spectroscopy of the wet material. The reaction follows a sigmoidal function indicative of a process of nucleation and growth and was modeled using the Avrami equation. Reaction rates and the dimensionality of growth (as indicated by the value of the Avrami constant) are strongly influenced by stirring rate. The reaction follows Arrhenius behavior, and there is a strong dependence of both the rate constant and the Avrami constant on acetate concentration. Acetate may act as a phase transfer catalyst, solubilizing hematin and facilitating its redeposition as beta-hematin. The pH dependence of the process indicates that only the monoprotonated species of hematin is active in forming beta-hematin. The formation of beta-hematin closely parallels many mineralization processes, and this suggests that hemozoin formation may be a unique biomineralization process. Inferences are drawn with respect to the formation of hemozoin in vivo.
利用定量红外光谱、X射线衍射、扫描和透射电子显微镜对酸性醋酸盐溶液中β-血红素的形成进行了研究。该过程通过无定形（或可能是纳米晶体）血红素的快速沉淀发生，随后缓慢转化为晶体β-血红素。湿材料的X射线衍射和红外光谱提供了确凿证据，表明该反应发生在醋酸盐介质孵育期间，而非干燥阶段。该反应遵循S形函数，表明是一个成核和生长过程，并使用阿弗拉米方程进行建模。搅拌速率对反应速率和生长维度（由阿弗拉米常数的值表示）有很大影响。该反应遵循阿伦尼乌斯行为，速率常数和阿弗拉米常数都强烈依赖于醋酸盐浓度。醋酸盐可能作为相转移催化剂，溶解血红素并促进其重新沉积为β-血红素。该过程对pH的依赖性表明，只有单质子化的血红素物种在形成β-血红素时具有活性。β-血红素的形成与许多矿化过程密切相似，这表明疟原虫色素的形成可能是一个独特的生物矿化过程。文中对体内疟原虫色素的形成进行了推断。
