Formate oxidation and oxygen reduction by leaf mitochondria.

Mitochondria isolated from the leaves of several plant species were investigated for the presence of NAD-linked formate dehydrogenase. The NADH produced was oxidized by the electron transport sequence and was coupled to ATP synthesis. The amounts of formate dehydrogenase, and, thereby, the capacity for formate-dependent O(2) uptake, varied greatly among species. While no activity was detectable in mitochondria from soybean leaves, the rate of formate oxidation by spinach mitochondria was about one-half the rate of malate oxidation. In spinach, only mitochondria from green tissues oxidized formate. These last two observations raise questions as to the role of this reaction and the possible sources of the formate metabolized.