Carbon isotope effects on the decarboxylation of carboxylic acids. Comparison of the lactate oxidase reaction and the degradation of pyruvate by H2O2.
The isotope effect at C-1 on the H2O2-catalysed decarboxylation of pyruvate (used as a model reaction for the enzymic reaction) increases between pH 3 and 10 from 1.0007 +/- 0.0004 to 1.0283 +/- 0.0014 (25 degrees C). This result indicates a change in the rate-determining step from formation of the tetrahedral intermediate to decarboxylation of this intermediate. Practically no isotope fractionation at C-1 (1.0011 +/- 0.0002, pH 6.0, 25 degrees C) is found in the lactate oxidase-catalysed decarboxylation of lactate, which is indicative for the existence of an irreversible O2-dependent step prior to the enzyme-catalysed decarboxylation. In addition, the result provides further evidence that dissociation of pyruvate and H2O2 from the enzyme can be excluded. The isotope effect at C-2 of lactate in the enzymic reaction (1.0048 +/- 0.0004) is attributed to the hydrogen transfer step from lactate to the coenzyme.
Melzer
E
E
Lehrstuhl für Allgemeine Chemie und Biochemie der Technischen Universität München, Freising-Weihenstepan, Federal Republic of Germany.
Schmidt
H L
HL
D002247:Carbon Isotopes; D003653:Decarboxylation; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007700:Kinetics; D008722:Methods; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D008956:Models, Chemical; D011773:Pyruvates / Q000378:metabolism*; D019289:Pyruvic Acid
D002247:Carbon Isotopes; D011773:Pyruvates; D019289:Pyruvic Acid; D006861:Hydrogen Peroxide; D006899:Mixed Function Oxygenases; C021497:lactate 2-monooxygenase