Comparison of electron transfer kinetics between redox proteins free in solution and electrostatically complexed to a lipid bilayer membrane.
Comparison of electron transfer kinetics between redox proteins free in solution and electrostatically complexed to a lipid bilayer membrane.
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溶液中游离的氧化还原蛋白和静电复合到脂质双层膜上的氧化还原蛋白之间的电子转移动力学比较。
DOI：
10.1006/abbi.1994.1183
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发表时间：
1994
影响因子：
3.9
通讯作者：
Tollin,G
中科院分区：
文献类型：
--
作者：
Cheddar,G;Tollin,G
在溶液中，马细胞色素c（cytc;净电荷+7）被拜氏梭菌铁氧还蛋白半醌（Fld;净电荷-16）或被还原的菠菜铁氧还蛋白（Fd;净电荷-15）还原的二级速率常数随着离子强度的增加而单调下降，正如对带相反电荷物种之间反应的预期。虽然Fld反应的速率常数在低离子强度下比Fd大几乎两个数量级，但外推到无限离子强度的值非常相似，表明当消除静电效应时具有可比的反应性。此外，Fld具有比Fd大得多的静电相互作用能值，因此具有更大的表观活性位点电荷，这是由于在低离子强度下的速率常数差异。在低离子强度下静电结合细胞色素c到带负电荷的脂质双层囊泡（含有卵磷脂（PC）和心磷脂（CL）的混合物的膜）导致观察到的电子转移速率常数（kobs）显着降低，用于通过Fld和Fd还原细胞色素。这种降低的幅度与膜中存在的CL的摩尔百分比成比例（在5-60摩尔%内变化10- 20倍）。随着Fld，kobs单调下降，增加离子强度在一个固定的CL浓度。随着Fd的增加inkobsocurs的离子强度增加，这最大化在中间离子强度在一个值大于在没有脂质囊泡的情况下获得的。当Fld静电结合到由40 mol%的双十八烷基二甲基铵离子（DODAC）和60 mol%的PC组成的带正电荷的囊泡时，电子转移到cytc的againkobs比在溶液中获得的减少，并且通过增加离子强度单调地减小幅度。相反，电子从Fd转移到cytc的kobs不受带正电荷的膜的存在的影响。这些结果的影响膜表面电荷在调节蛋白质-蛋白质相互作用的作用进行了讨论。
The second-order rate constants obtained in solution for the reduction of horse cytochrome c (cytc; net charge +7) by eitherClostridium beijerinckiiflavodoxin semiquinone (Fld; net charge −16) or reduced spinach ferredoxin (Fd; net charge −15) decrease monotonically with increasing ionic strength, as expected for reactions between oppositely charged species. Although the rate constant for the Fld reaction is almost two orders of magnitude larger at low ionic strength than that for Fd, the values extrapolated to infinite ionic strength are closely similar, indicating comparable reactivities when electrostatic effects are eliminated. Furthermore, Fld has a much larger value for the electrostatic interaction energy, and thus a larger apparent active site charge, than does Fd, accounting for the rate constant disparity at low ionic strength. Electrostatically binding cytc at low ionic strength to a negatively charged Lipid bilayer vesicle (membranes containing mixtures of egg phosphatidylcholine (PC) and cardiolipin (CL)) results in a marked decrease of the observed electron transfer rate constant (kobs) for reduction of the cytochrome by both Fld and Fd. The magnitude of this decrease is proportional to the mole percent of CL present in the membrane (10- to 20-fold change over 5-60 mol%). With Fld,kobsdecreases monotonically with increasing ionic strength at a fixed CL concentration. With Fd an increase inkobsoccurs as the ionic strength is increased, which maximizes at intermediate ionic strength at a value larger than that obtained in the absence of lipid vesicles. When Fld is electrostatically bound to a positively charged vesicle composed of 40 mol% dioctadecyldimethylammonium ion (DODAC) and 60 mol% PC, againkobsfor electron transfer to cytc is decreased over that obtained in solution, and the magnitude is diminished monotonically by increasing ionic strength. In contrast,kobsfor electron transfer from Fd to cytc is unaffected by the presence of the positively charged membrane. The implications of these results for the role of membrane surface charge in modulating protein-protein interactions is discussed.