Transient kinetics of electron transfer from a variety of c-type cytochromes to plastocyanin.
Transient kinetics of electron transfer from a variety of c-type cytochromes to plastocyanin.
复制标题
从各种 c 型细胞色素到质体蓝素的电子转移的瞬时动力学。
DOI：
10.1021/bi00068a010
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发表时间：
1993
期刊：
影响因子：
2.9
通讯作者：
Tollin,G
中科院分区：
文献类型：
--
作者：
Meyer,TE;Zhao,ZG;Cusanovich,MA;Tollin,G
摘要：质体蓝素（PC）和它的生理反应伴侣细胞色素（cyt）f形成一种复合物，这种复合物通过互补局部电荷之间的相互作用而静电稳定。我们用激光闪光光解法测定了几种还原型细胞色素与PC之间的复合物内电子转移动力学。对于菠菜cyt/和菠菜PC，我们获得了可逆反应的一级速率常数，kf 0 rward = 2780 s-1和kreverse= 1050 s-1，以及在5 mM的离子强度（7）下约23 µ的络合物解离常数。观察到的速率常数在I=5和40 mM之间增加2倍，然后在更高的离子强度下单调下降。这表明复合物直到π = 150 mM才完全解离，并且静电最稳定的复合物内的蛋白质对于电子转移不是最佳取向的。用芜菁细胞色素f和菠菜PC得到了类似的结果，尽管在这种情况下复合物内的电子转移快约4倍。马cyt c也能与PC形成静电稳定的复合物，复合物内电子转移的极限速率常数（1750 s_1）和解离常数（10 µ）与菠菜cyt/相当。离子强度的依赖性表明，该复合物更容易解离（在7= 25 mM时完成）比细胞色素F和重排是不是requiredfor最佳的电子转移。多聚赖氨酸的加入导致电子转移速率的10倍抑制。假单胞菌cyt c-551是一种酸性细胞色素，不与PC形成复合物。与PC反应的二级速率常数在7= 5 mM时比cyt f或cyt c小约2个数量级，并且增加离子强度对cyt c-551反应的影响是单调增加速率常数。添加聚赖氨酸也导致速率常数的增加，这在幅度上与离子强度引起的速率常数相当。Chlorobium cyt c-555是一种碱性蛋白质，但动力学结果表明，它不与PC形成复合物，尽管二级速率常数与其他碱性细胞色素相似。离子强度的影响是以与简单静电理论一致的方式单调降低速率常数。对于所有的细胞色素，速率常数外推到无限的离子强度是可比的大小。然而，蛋白质-蛋白质电子转移速率常数应与热力学驱动力，如果距离和取向保持不变。事实上，他们不建议，这些因素不同的细胞色素在其与PC的反应。
Revised Manuscript Received February 18, 1993 abstract: Plastocyanin (PC) and its physiological reaction partner cytochrome (cyt) f form a complex which is electrostatically stabilized by interactions between complementary localized charges. We have measured the kinetics of intracomplex electron transfer between several reduced cytochromes and PC using laser flash photolysis. With spinach cyt/and spinach PC, we obtain first-order rate constants, kf0rward= 2780 s-1 and kreverse= 1050 s~\for the reversible reaction and a complex dissociation constant of about 23 µ at an ionic strength (7) of 5 mM. The observed rate constant increases by a factor of 2 between I=5 and 40 mM and then decreases monotonically at higher ionic strengths. This indicates that the complex is not completely dissociated until 7= 150 mM and that the proteins within the electrostatically most stable complex are not optimally oriented for electron transfer. Similar results were obtained with turnip cyt f and spinach PC, although in this case intracomplex electron transfer is about 4 times as fast. Horse cyt c also forms an electrostatically stabilized complex with PC, andyields a limiting rate constant for intracomplex electron transfer (1750 s_1) and a dissociation constant (10 µ) comparable to those for spinach cyt/. The ionic strength dependence shows that the complex is more readily dissociated (complete at 7= 25 mM) than is that of cyt f and that rearrangement is not requiredfor optimal electron transfer. Addition of polylysine results in 10-fold inhibition of the rate of electron transfer. Pseudomonas cyt c-551is an acidic cytochrome which does not form a complex with PC. The second-order rate constant for reaction with PC at 7= 5 mM is about 2 orders of magnitude smaller than for cyt f or cyt c, and the effect of increasing ionic strength on the cyt c-551 reaction is to monotonically increase the rate constant. Addition of polylysine also results in an increase in the rate constant, which is comparable in magnitude to that caused by ionic strength. Chlorobium cyt c-555 is a basic proteinlike horse cyt c, but the kinetic results indicate that it does not form a complex with PC, although the second-order rate constant is similar to those obtained with the other basic cytochromes. The effect of ionic strength is to monotonically decrease the rate constant in a manner consistent with simple electrostatic theory. Forall of the cytochromes, the rate constants extrapolated to infinite ionic strength are comparable in magnitude. However, protein-protein electron-transfer rate constants should correlate with the thermodynamic driving force if the distances and orientations are held constant. The fact that they do not suggests that these factors vary for the different cytochromes in their reactions with PC.