LoBrutto R, Wei Y H, Yoshida S, Van Camp H L, Scholes C P, King T E
Biophys J. 1984 Feb;45(2):473-9. doi: 10.1016/S0006-3495(84)84171-5.
By the electron paramagnetic resonance (EPR) technique, recovery kinetics for nitric oxide (NO) to heme following cryogenic photolysis were studied for the nitrosylferrocytochrome a3 center in cytochrome c oxidase and for myoglobin. The recovery was nonexponential, as has been observed in previous cryogenic CO and O2 rebinding to heme systems. NO rebinding to heme a3 started near a temperature of 50 K and was related to a distribution of thermal activation energies. At the peak of the distribution the activation energy was 3.1 kcal/mol, and the preexponential in the recovery rate was 10(9.9) s-1. For recovery of NO back to the a3 heme, the activation energy was threefold less than that for CO where CO binds to nearby Cua3 following photolysis from heme a3, but was larger than the activation energy for CO, O2, and probably NO rebinding to myoglobin. NO ligand rebinding to myoglobin occurred at a temperature as low as 15 K and in a temperature regime where tunneling could occur. However, the rate of NO rebinding to myoglobin did increase with temperature in the 15-25 K range.
通过电子顺磁共振（EPR）技术，研究了细胞色素c氧化酶中亚硝酰亚铁细胞色素a3中心以及肌红蛋白中，低温光解后一氧化氮（NO）与血红素的恢复动力学。这种恢复是非指数性的，正如之前在低温下CO和O2与血红素系统重新结合时所观察到的那样。NO与血红素a3的重新结合在接近50K的温度下开始，并且与热活化能的分布有关。在分布峰值处，活化能为3.1千卡/摩尔，恢复速率中的指数前因子为10(9.9) s-1。对于NO恢复到a3血红素的过程，活化能比CO从血红素a3光解后与附近的Cua3结合时的活化能小三倍，但比CO、O2以及可能的NO与肌红蛋白重新结合的活化能大。NO配体与肌红蛋白的重新结合在低至15K的温度下发生，且处于可能发生隧穿的温度范围。然而，在15 - 25K范围内，NO与肌红蛋白重新结合的速率确实随温度升高。
