Oxidation of Proline by Plant Mitochondria

Mitochondria isolated from etiolated shoots of corn (Zea mays), wheat (Triticum aestivum), barley (Hordeum vulgare), soybean (Glycine max L. Merr.), and mung bean (Phaseolus aureus) exhibited a proline-dependent O(2) uptake subject to respiratory control. ADP/O ratios with proline as substrate were intermediate between ratios obtained with exogenous NADH and malate + pyruvate as substrates. Isotope studies showed proline metabolism to be dependent on O(2), but not NAD. The major ninhydrin-positive product formed via Delta(1)-pyrroline-5-carboxylic acid was glutamate. Mitochondria were capable of further metabolism of glutamate, as radioactive CO(2), organic acids, and aspartate were recovered after [(14)C]proline feeding experiments. These results demonstrate the mitochondrial association and O(2) dependence of plant proline metabolism.