Equilibrium carbon isotope effect on a decarboxylation reaction

Carbon isotope exchange equilibrium between carbon dioxide and the β-carboxyl carbon of D-isocitric acid has been achieved by means of the enzyme isocitrate dehydrogenase. Measurements of the isotopic compositions at these two sites reveal that the carboxyl carbon is enriched in ¹³C relative to carbon dioxide. The isotope exchange equilibrium constant is 1.0027 at 25°, pH 7.5.