Kinetics of nitric oxide dissociation from five- and six-coordinate nitrosyl hemes and heme proteins, including soluble guanylate cyclase
Kinetics of nitric oxide dissociation from five- and six-coordinate nitrosyl hemes and heme proteins, including soluble guanylate cyclase
复制标题
DOI：
10.1021/bi970201o
复制
发表时间：
1997-06-03
期刊：
影响因子：
2.9
通讯作者：
Koesling, D
中科院分区：
文献类型：
--
作者：
Kharitonov, VG;Sharma, VS;Koesling, D
NO解离动力学的特点是三个五坐标系统，血红素-NO，HSA-血红素-NO（人血清白蛋白），GC-NO（可溶性鸟苷酸环化酶），并为六坐标系统，IM-血红素-NO。亚硝基肌红蛋白进行了重新测定比较。先前已知的六配位R和T状态亚硝酰血红蛋白也包括在比较中。数据表明，NO从五坐标模型血红素解离的速度比从六坐标类似物解离的速度快1000倍以上。NO和近端碱基之间的这种负反式效应与羧基血红素衍生物形成鲜明对比，其中当存在反式碱基时，配体解离速率大大减慢。由于反式效应相反，六配位羧基和亚硝酰基衍生物具有可比的解离速率，即使五配位物种非常不同。在蛋白质中，五配位形式和六配位形式在解离速率上没有很大的差异。部分原因可能是由于不同蛋白质中成对重组的概率不同，但这不能解释所有的事实。蛋白质结构本身也必然对键断裂速率常数产生影响。除了血红蛋白处于T状态外，亚硝酰鸟苷酸环化酶显示出最高的NO解离速率常数，k（obs）= 6 × 10（-4）s（-1）。这将产生在37 ℃下从GC-NO解离NO的半衰期约为2分钟，这个数字对这种关键血红素酶的活性调节机制具有意义。
Kinetics of NO dissociation were characterized for three five-coordinate systems, heme-NO, HSA-heme-NO (human serum albumin), GC-NO (soluble guanylate cyclase), and for the six-coordinate system, Im-heme-NO. Nitrosyl myoglobin was redetermined for comparison. Previously known, six-coordinate R and T state nitrosyl hemoglobins are also included in the comparison. The data indicate that NO dissociates more than 1000 times faster from five-coordinate model heme than it does from the six-coordinate analog. Such a negative trans-effect between NO and a proximal base is in sharp contrast to carboxy heme derivatives, in which ligand dissociation rates are greatly slowed in when a trans base is present. As a result of opposite trans-effects, six-coordinate carboxy and nitrosyl derivatives have comparable dissociation rates, even though the five-coordinate species are very different. In proteins, five- and six-coordinate forms do not show a large difference in dissociation rates. Part of the reason may be due to different probabilities for geminate recombination in the different proteins, but this cannot explain all the facts. There must also be influences of the protein structure on bond-breaking rate constants themselves. With the exception of hemoglobin in the T state, nitrosyl guanylate cyclase shows the highest NO dissociation rate constant, k(obs) = 6 x 10(-4) s(-1) This would yield a half-life of about 2 min at 37 degrees C for dissociation of NO from GC-NO, a number that has implications for the mechanism of regulation of the activity of this key heme enzyme.