Activity of the mitochondrial pyruvate dehydrogenase complex in plants is stimulated in the presence of malate

• Malate activates plant mitochondrial pyruvate dehydrogenase complex (PDC).
• Stimulation by malate is related to а partially activated PDC.
• No stimulation of chloroplast PDC by malate is observed.
• Malate reversed the reduction in PDC activity in the presence of glycine.
• Malate effect on PDC involves establishment of malate dehydrogenase equilibrium.

The effect of malate on the steady-state activity of the pea (Pisum sativum L.) and barley (Hordeum vulgare L.) leaf pyruvate dehydrogenase complex (PDC) has been studied in isolated mitochondria. The addition of malate was found to be stimulatory for the mitochondrial PDC, however there was no stimulation of chloroplast PDC. The stimulation was saturated below 1 mM malate and was apparently related to а partially activated complex, which activity increased in the presence of malate by about twofold. Malate also reversed the reduction of PDC activity in the presence of glycine. Based on the obtained kinetic data, we suggest that the effect of malate is rather not a direct activation of PDC but involves the establishment of NAD-malate dehydrogenase equilibrium, decreasing concentration of NADH and relieving its inhibitory effect of PDC.