Experimental Evidence for a Hydride Transfer Mechanism in Plant Glycolate Oxidase Catalysis [Plant Biology]

November 21st, 2014 by Dellero, Y., Mauve, C., Boex-Fontvieille, E., Flesch, V., Jossier, M., Tcherkez, G., Hodges, M.

In plants, glycolate oxidase is involved in the photorespiratory cycle, one of the major fluxes at the global scale. To clarify both the nature of the mechanism and possible differences in glycolate oxidase enzyme chemistry from C3 and C4 plant species, we analyzed kinetic parameters of purified recombinant C3 (Arabidopsis thaliana) and C4 (Zea mays) plant enzymes, and compared isotope effects using natural and deuterated glycolate, in either natural or deuterated solvent. The 12C/13C isotope effect was also investigated for each plant glycolate oxidase protein by measuring the 13C natural abundance in glycolate, using natural or deuterated glycolate as a substrate. Our results suggest that several elemental steps were associated with an H/D isotope effect and that glycolate α-deprotonation itself was only partially rate-limiting. Calculations of commitment factors from observed kinetic isotope effect values support a hydride transfer mechanism. No significant differences were seen between C3 and C4 enzymes.