Szebeni J, Hauser H, Eskelson C D, Watson R R, Winterhalter K H
Department of Physiology, National Institute of Food Hygiene and Nutrition, Budapest, Hungary.
Biochemistry. 1988 Aug 23;27(17):6425-34. doi: 10.1021/bi00417a034.
Hemoglobin (Hb) was incubated with small unilamellar vesicles of different lipid compositions in physiological or low pH-low ionic strength media, and the alterations in the protein and bilayer structure were analyzed by measuring (i) the sedimentation properties and elution pattern of the vesicles upon gel filtration, (ii) the quenching effect of Hb on the fluorescence of membrane-embedded probes, (iii) the intrinsic fluorescence of Hb, and (iv) the Soret spectra of Hb. The results indicate complex formation between Hb and the membrane, followed by intercalation of the protein into the bilayer. These processes can lead to secondary alterations, including aggregation, peroxidative decomposition of unsaturated fatty acids, unfolding of Hb, oxidation of the heme iron, displacement of the heme relative to globin, and oxidative or nonoxidative deconjugation of the porphyrin ring. Complex formation and intercalation of Hb into the bilayer are primarily due to hydrophobic interaction between the protein and the membrane, whereas displacement of the heme and its nonoxidative deconjugation are elicited by ionic interaction between the heme and negative membrane surface charges. These charges, on the other hand, inhibit the oxidative processes in unsaturated lipid vesicles. The rate and extent of alterations both in the protein and in the membrane show inverse correlation with the stability of the heme-globin linkage. The liquid-crystalline phase state promotes the penetration of Hb into the bilayer, whereas displacement of the heme is most expressed in the case of saturated bilayers in the gel state. Cholesterol inhibits both the hydrophobic and ionic interactions between the protein and bilayer, most remarkably the partition of the heme into negatively charged saturated bilayers. It is suggested that the effects of cholesterol are mediated through changes in membrane fluidity.
将血红蛋白（Hb）与不同脂质组成的小单层囊泡在生理或低pH - 低离子强度介质中孵育，通过测量以下指标分析蛋白质和双层结构的变化：（i）凝胶过滤时囊泡的沉降特性和洗脱模式；（ii）Hb对膜嵌入探针荧光的猝灭作用；（iii）Hb的内在荧光；（iv）Hb的Soret光谱。结果表明Hb与膜之间形成复合物，随后蛋白质插入双层膜中。这些过程会导致二级变化，包括聚集、不饱和脂肪酸的过氧化分解、Hb的展开、血红素铁的氧化、血红素相对于珠蛋白的位移以及卟啉环的氧化或非氧化解偶联。Hb与双层膜的复合物形成和插入主要是由于蛋白质与膜之间的疏水相互作用，而血红素的位移及其非氧化解偶联是由血红素与膜负表面电荷之间的离子相互作用引起的。另一方面，这些电荷抑制不饱和脂质囊泡中的氧化过程。蛋白质和膜中变化的速率和程度与血红素 - 珠蛋白连接的稳定性呈负相关。液晶相状态促进Hb渗透到双层膜中，而血红素的位移在凝胶态的饱和双层膜中最为明显。胆固醇抑制蛋白质与双层膜之间的疏水和离子相互作用，最显著的是血红素在带负电荷的饱和双层膜中的分配。有人认为胆固醇的作用是通过膜流动性的变化介导的。
