The control of the oxidation of proline by isolated flight muscle mitochondria.

The oxidation of proline by blowfly (Phormia regina) flight muscle mitochondria is stimulated by ADP in the presence of oligomycin. The stimulation is enhanced by high levels of Pi, is still evident with intact mitochondria in the presence of rotenone, arsenate, or arsenite, and is seen with sonically treated particles. The findings indicate that the site of action of the nucleotide is L-proline : cytochrome c oxidoreductase (proline dehydrogenase). It is suggested that ADP is an allosteric effector of the dehydrogenase and lowers the apparent K, for proline. The Km in the presence of ADP approximates the concentration of proline found in the flight muscle at rest. Pyruvate also increases the affinity of the proline dehydrogenase for its substrate. The rate of proline oxidation is dependent on the relative proportions of the adenine nucleotides as well as on the absolute level of ADP. Sensitivity to ADP in the presence of an uncoupling agent or atractyloside suggests that there is an external site for ADP. The physiological significance of the activation of proline oxidation is considered.