Studies on the inner mitochondrial membrane localization of proline dehydrogenase.

1. The site of proline dehydrogenase (EC 1.5.99.-) activity in blowfly (Phormia regina) flight muscle mitochondria has been investigated employing the inner membrane-impermeable Fe(CN)63-as electron acceptor. Antimycin had no inhibitory effect on ferricyanide reduction due to proline dehydrogenase activity. Ferricyanide reductase activity due to inside localized dehydrogenase activity was antimycin sensitive. These results indicate that the interaction between proline dehydrogenase and ferricyanide was direct and not dependent on respiratory chain activity. 2. The stimulatory action of the effector, ADP, on proline dehydrogenase activity was insensitive to atractyloside, an indication that the site of dehydrogenase interaction with ADP was external to the atractyloside barrier. 3. Swelling studies revealed that proline does not readily penetrate the matrix space. 4. An outside localization for proline dehydrogenase is discussed in terms of the role of proline in insect flight muscle metabolism.