The function of glycine decarboxylase complex is optimized to maintain high photorespiratory flux via buffering of its reaction products

• Glycine oxidation in plant mitochondria is facilitated by recycling of its products.
• Maintenance of low levels of NADH and CO2 prevents glycine decarboxylase inhibition.
• Malate dehydrogenase and carbonic anhydrase recycle photorespiratory NADH and CO2.
• Glycine oxidation engages rotenone-insensitive dehydrogenases and alternative oxidase.

Oxidation of glycine in photorespiratory pathway is the major flux through mitochondria of C3 plants in the light. It sustains increased intramitochondrial concentrations of NADH and NADPH, which are required to engage the internal rotenone-insensitive NAD(P)H dehydrogenases and the alternative oxidase. We discuss here possible mechanisms of high photorespiratory flux maintenance in mitochondria and suggest that it is fulfilled under conditions where the concentrations of glycine decarboxylase reaction products NADH and CO2 achieve an equilibrium provided by malate dehydrogenase and carbonic anhydrase, respectively. This results in the removal of these products from the glycine decarboxylase multienzyme active sites and in the maintenance of their concentrations at levels sufficiently low to prevent substrate inhibition of the reaction.