Quantum mechanical hydrogen tunneling in bacterial copper amine oxidase reaction.
A key step decisively affecting the catalytic efficiency of copper amine oxidase is stereospecific abstraction of substrate alpha-proton by a conserved Asp residue. We analyzed this step by pre-steady-state kinetics using a bacterial enzyme and stereospecifically deuterium-labeled substrates, 2-phenylethylamine and tyramine. A small and temperature-dependent kinetic isotope effect (KIE) was observed with 2-phenylethylamine, whereas a large and temperature-independent KIE was observed with tyramine in the alpha-proton abstraction step, showing that this step is driven by quantum mechanical hydrogen tunneling rather than the classical transition-state mechanism. Furthermore, an Arrhenius-type preexponential factor ratio approaching a transition-state value was obtained in the reaction of a mutant enzyme lacking the critical Asp. These results provide strong evidence for enzyme-enhanced hydrogen tunneling. X-ray crystallographic structures of the reaction intermediates revealed a small difference in the binding mode of distal parts of substrates, which would modulate hydrogen tunneling proceeding through either active or passive dynamics.
Department of Structural Molecular Biology, Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan.
Takeshi
T
Murakawa
Toshihide
T
Okajima
Shun'ichi
S
Kuroda
Takuya
T
Nakamoto
Masayasu
M
Taki
Yukio
Y
Yamamoto
Hideyuki
H
Hayashi
Katsuyuki
K
Tanizawa
D006631:Amine Oxidase (Copper-Containing) / Q000737:chemistry* / Q000378:metabolism*; D019943:Amino Acid Substitution / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003903:Deuterium / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D009154:Mutation; D010084:Oxidation-Reduction; D010627:Phenethylamines / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
C086758:2,4,5-trihydroxyphenylalanine quinone; D001426:Bacterial Proteins; D010627:Phenethylamines; D004295:Dihydroxyphenylalanine; D003903:Deuterium; D006631:Amine Oxidase (Copper-Containing)