Insights into the nature of the hydrogen bonding of *Tyr272 in apo-galactose oxidase.
The synthesis and structure of an o-methylthio-phenol-imidazole, 2-(2'-(4'-tert-butyl-6'-methylsulfanyl)-hydroxyphenyl))-4,5-diphenyl-imidazole ((MeS)LH), is reported; X-ray crystallographic studies have shown that (MeS)LH involves an O-H...N(+) hydrogen bond between the phenol and an imidazole nitrogen. (MeS)LH undergoes a reversible, one-electron, oxidation to form the radical cation [(MeS)LH](*)(+) the EPR spectrum of which is remarkably similar to that of (*)Tyr(272) in Cu-free, oxidized, apo-GO. Density Functional Theory calculations, have shown that the proton-transferred (R-O(*)...H-N(+)) form of [(MeS)LH](*)(+) has a spin density distribution--with a substantial delocalization of the unpaired electron spin density onto the ortho sulfur atom--and EPR properties that are in good agreement with those of (*)Tyr(272) in Cu-free, oxidized, apo-GO whereas the non-proton-transferred (R-O(*)(+)-H...N) form does not. The results reported herein are a further demonstration of the influence of hydrogen bonding on the nature and properties of phenoxyl radicals and strongly suggest that the phenoxyl oxygen of (*)Tyr(272) in Cu-free, oxidized, apo-GO is involved in a O(*)...H-O/N hydrogen bond.
Benisvy
Laurent
L
Max-Planck-Instut für Bioanorganische Chemie, Stiftstrasse 34-46, Mülheim an der Ruhr, D45470, Germany. benisvy@yahoo.com
Hammond
Deborah
D
Parker
David J
DJ
Davies
E Stephen
ES
Garner
C David
CD
McMaster
Jonathan
J
Wilson
Claire
C
Neese
Frank
F
Bothe
Eberhard
E
Bittl
Robert
R
Teutloff
Christian
C
D018360:Crystallography, X-Ray; D004563:Electrochemistry; D005692:Galactose Oxidase / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry*