title: Concerning the mechanism for transfer of D-glucuronate from myo-inositol oxygenase to D-glucuronate reductase.
abstract: The D-glucuronate product of myo-inositol oxygenase (EC 1.13.99.1) is efficiently reduced by NADPH in the presence of either purified D-glucuronate reductase (EC 1.1.1.19), or reductase that is part of a protein aggregate that also contains the oxygenase. This occurs despite the fact that the maximum concentration of D-glucuronate that could be formed by the oxygenase under the conditions used for the coupled enzyme experiments is 7 microM, and 10 microM externally supplied D-glucuronate (Km = 7.6 mM) does not support any detectable NADPH oxidation under the reaction conditions. The most likely explanation for the results is that the uncyclized aldehyde form of D-glucuronate is the product of the oxygenase reaction, and that it diffuses into solution and is captured by the reductase before it cyclizes to the more stable but less reactive hemiacetal form.
mesh_terms: D002237:Carbohydrate Dehydrogenases / Q000378:metabolism*; D005965:Glucuronates / Q000378:metabolism*; D020723:Glucuronic Acid; D050562:Inositol Oxygenase; D007700:Kinetics; D009249:NADP; D010101:Oxygen Consumption; D010105:Oxygenases / Q000378:metabolism*
chemical_list: D005965:Glucuronates; D009249:NADP; D020723:Glucuronic Acid; D002237:Carbohydrate Dehydrogenases; C020590:L-glucuronate reductase; D010105:Oxygenases; D050562:Inositol Oxygenase