Evidence for protein radical-mediated nuclear tunneling in fatty acid alpha-oxygenase.
Rice alpha-oxygenase (RalphaO) catalyzes the insertion of O2 into the Calpha-H bond of various fatty acids. The mechanism is thought to involve a tyrosyl radical as the oxidant on the basis of comparisons to the structurally homologous cyclooxygenase enzymes. Kinetic and spectroscopic results presented here for the wild-type RalphaO and the Tyr379Phe mutant indicate an irreversible H* abstraction mechanism and support the involvement of the proposed catalytic Tyr*. In addition, very large, weakly temperature dependent deuterium kinetic isotope effects (approximately 50) are observed, consistent with extensive nuclear tunneling. RalphaO, thus, presents a novel example where such quantum effects are associated with an amino acid radical-utilizing enzyme.
Gupta
Ankur
A
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore Maryland 21218, USA.
Mukherjee
Arnab
A
Matsui
Kenji
K
Roth
Justine P
JP
D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D003903:Deuterium / Q000737:chemistry; D005227:Fatty Acids / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D012275:Oryza / Q000201:enzymology*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D013057:Spectrum Analysis; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
D005227:Fatty Acids; D005609:Free Radicals; D011506:Proteins; D014443:Tyrosine; D010649:Phenylalanine; D002244:Carbon; D006859:Hydrogen; D003903:Deuterium; D010105:Oxygenases; C426838:fatty acid alpha-hydroperoxylase; D010100:Oxygen