Pyrroloquinoline quinone as cofactor in galactose oxidase (EC 1.1.3.9).
Galactose oxidase from Dactylium dendroides was shown to contain one molecule of covalently bound pyrroloquinoline quinone (PQQ/enzyme molecule. From the spectroscopic characteristics reported for the enzyme forms, a mechanistic role for PQQ could be deduced. In analogy with other quinoproteins, the initial formation of a PQQ-substrate adduct is proposed. Following internal hydrogen transfer, leading to aldehyde product and reduced pyrroloquinoline quinone, reoxidation of the organic cofactor with molecular oxygen could be mediated by the PQQ-liganded copper ion with concomitant formation of hydrogen peroxide. With PQQ as an additional (two-electron) redox center the occurrence of a "superoxidized" enzyme form must be considered. Possible consequences of this view, in relation to a physiological function of the enzyme and interpretation of ESR data, are discussed.
van der Meer
R A
RA
Department of Microbiology and Enzymology, Delft University of Technology, The Netherlands.
Jongejan
J A
JA
Duine
J A
JA
D003300:Copper / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005658:Fungi / Q000201:enzymology; D005692:Galactose Oxidase / Q000032:analysis* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045542:PQQ Cofactor; D015363:Quinolones / Q000032:analysis* / Q000378:metabolism; D013053:Spectrophotometry
D015363:Quinolones; D045542:PQQ Cofactor; D003300:Copper; D006861:Hydrogen Peroxide; D005692:Galactose Oxidase; D010100:Oxygen