Picosecond Dynamics of Photoexcited DNO-Bound Myoglobin Probed by Femtosecond Vibrational Spectroscopy
详细信息 查看全文
- 作者：Taegon Lee ; Sungu Hwang ; Manho Lim
- 刊名：Journal of Physical Chemistry B
- 出版年：2015
- 出版时间：February 5, 2015
- 年：2015
- 卷：119
- 期：5
- 页码：1814-1822
- 全文大小：393K
- ISSN：1520-5207
文摘
Like nitric oxide (NO), nitroxyl (HNO), a reduced form of NO, plays many biologically important roles including neurological function and vascular regulation. Although HNO is unstable in aqueous solution, it is exceptionally stable on binding to ferrous myoglobin (Mb) to form MbHNO. Various experimental and theoretical investigations has been carried out to unveil the structure of the active site and binding characteristics of MbHNO that can explain its functioning mechanism and the origin of its unusual stability. However, the binding dynamics of HNO to Mb, as well as the photochemical and photophysical processes associated with binding, have not been fully established. Herein, femtosecond vibrational spectroscopy was used to probe the photoexcitation dynamics of excited MbDNO in D2O solution at 294 K with a 575 nm pulse. Time-resolved spectra were described by three vibrational bands near 1380 cm鈥?, in the expected N鈥揙 stretching (谓N鈥揙) mode of MbDNO, and all three bands showed instantaneous bleach that decays on a picosecond time scale. The three bands were assigned based on isotope shifts upon 15N substitution and ab initio calculation of the vibrational frequency on a DNO-bound model heme. These three bands likely arise from Fermi interactions between the strong 谓N鈥揙 mode and the weak overtone and combination modes of the N atom-related modes. The immediate appearance of the bleach in these bands and the picosecond decay of the bleach indicate that most of the photoexcited MbDNO undergoes picosecond geminate rebinding (GR) of DNO to Mb subsequent to its immediate deligation. Ultrafast and efficient GR of DNO likely arises from the bonding structure of the ligand and high reactivity between DNO and Mb.