Intramolecular electron transfer rate between active-site copper and topa quinone in pea seedling amine oxidase.
The equilibrium between the two substrate-reduced forms of pea seedling amine oxidase, one containing Cu(II) and reduced 3-(2,4,5-trihydroxyphenyl)-L-alanine (topa) cofactor and one containing Cu(I) and topa semi-quinone, was investigated by visible spectroscopy as a function of temperature. To determine the rate of interconversion between the two species, temperature jump relaxation studies were performed on the substrate-reduced enzyme near room temperature. The yellow radical species was found to approach its equilibrium concentration with a maximum rate constant of 43,000 +/- 3,000 s-1. This rapid equilibration is attributed to intramolecular electron transfer between copper and topa. The data indicate that the Cu(I)/topaSQ species is a kinetically competent intermediate in the reaction of amine oxidases with substrates. Furthermore, the extremely rapid electron transfer rate (kET congruent to 20,000 s-1) suggests that the topa cofactor is in close proximity to the copper atom.
Turowski
P N
PN
Department of Chemistry, Amherst College, Massachusetts 01002-5000.
McGuirl
M A
MA
Dooley
D M
DM
D006631:Amine Oxidase (Copper-Containing); D001665:Binding Sites; D003300:Copper / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism; D004579:Electron Transport; D007887:Fabaceae / Q000201:enzymology*; D007700:Kinetics; D008961:Models, Structural; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism*; D010946:Plants, Medicinal; D013053:Spectrophotometry
D004295:Dihydroxyphenylalanine; C067626:6-hydroxydopa quinone; D003300:Copper; D006631:Amine Oxidase (Copper-Containing); D000587:Oxidoreductases Acting on CH-NH Group Donors