PMID- 16853859
OWN - NLM
STAT- MEDLINE
DCOM- 20070719
LR  - 20131121
IS  - 1520-6106 (Print)
IS  - 1520-5207 (Linking)
VI  - 109
IP  - 46
DP  - 2005 Nov 24
TI  - Structural character and energetics of tyrosyl radical formation by 
      electron/proton transfers of a covalently linked histidine-tyrosine: a model for 
      cytochrome C oxidase.
PG  - 22013-26
AB  - The structural, energetic, and electronic and IR spectroscopic properties for a 
      model of the cross-linked histidine-tyrosine (His-Tyr) residues as found in 
      cytochrome c oxidase (CcO) are investigated by ab initio methods. The formation 
      of a His-Tyr radical is studied by two paths: proton release followed by electron 
      release and vice versa. The energetics for the proton/electron releases of the 
      Tyr depend modestly on the cross-linked His substituent and, more sensitively, on 
      the charge of the cation attached to the imino N site of the His residue. 
      Protonation of the imino N site significantly increases the electron ionization 
      potential and decreases the proton dissociation energy, making them competitive 
      processes. A positive charge placed at the imino N site, whose value is scanned 
      from zero to one, shows a continuous increase in ionization potential and a 
      decrease in proton dissociation energy, with the +1 limit agreeing well with the 
      protonated imino N site result, indicating a dominant electrostatic effect. The 
      charge populations and the spin density distributions of the His-Tyr model, the 
      radical cation formed by electron ionization, the anion formed by proton 
      dissociation, and the final His-Tyr radical depend sensitively on the 
      substituents, implying a modulation role on the charge transfer between the 
      phenol and imidazole rings, especially for the charged species. His-Tyr and 
      protonated His-Tyr exhibit differences among their respective structural isomers 
      with consequences on their IR absorptions. Small barriers between their 
      pseudo-cis and pseudo-trans rotamers demonstrate the relative flexibility between 
      the two rings, and these may facilitate proton release and charge transfer. The 
      cation effect demonstrates that the cationized cross-linked His-Tyr should be the 
      best candidate to mimic the covalently ring-linked histidine-tyrosine structure 
      in CcO.
FAU - Bu, Yuxiang
AU  - Bu Y
AD  - Department of Chemistry, Michigan State University, East Lansing, Michigan 
      48824-1322, USA.
FAU - Cukier, R I
AU  - Cukier RI
LA  - eng
GR  - GM62790/GM/NIGMS NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PL  - United States
TA  - J Phys Chem B
JT  - The journal of physical chemistry. B
JID - 101157530
RN  - 0 (Free Radicals)
RN  - 0 (Protons)
RN  - 42HK56048U (Tyrosine)
RN  - 4QD397987E (Histidine)
RN  - EC 1.9.3.1 (Electron Transport Complex IV)
SB  - IM
MH  - Electron Transport Complex IV/*chemistry
MH  - Electrons
MH  - Free Radicals/chemical synthesis/chemistry
MH  - Histidine/*chemistry
MH  - *Models, Chemical
MH  - Molecular Structure
MH  - Protons
MH  - Tyrosine/*analogs & derivatives/*chemical synthesis/chemistry
EDAT- 2006/07/21 09:00
MHDA- 2007/07/20 09:00
CRDT- 2006/07/21 09:00
PHST- 2006/07/21 09:00 [pubmed]
PHST- 2007/07/20 09:00 [medline]
PHST- 2006/07/21 09:00 [entrez]
AID - 10.1021/jp053046t [doi]
PST - ppublish
SO  - J Phys Chem B. 2005 Nov 24;109(46):22013-26. doi: 10.1021/jp053046t.