ENERGETICS OF PROLINE TRANSPORT IN CORN MITOCHONDRIA

The mechanism of proline entry into the matrix region of isolated corn mitochondria (Z. mays L. Mo17 .times. B73) was investigated by measuring osmotically induced changes of mitochondrial size (changes in A520) in combination with O2 uptake measurements. Using NADH oxidation to generate the electrochemical gradient, proline transport was stereospecific, and could be inhibited by the proline analog L-thiazolidine-4-carboxylic acid. The energetics of proline transport were investigated by measuring the effects of FCCP (p-trifluoromethoxycarbonyl cyanide phenylhydrazone) and valinomycin on mitochondrial swelling and substrate oxidation. Proline transport and the resulting oxidation were partially dependent upon the energy of the electrochemical gradient. At low proline concentrations, entry was primarily independent of the gradient (based on insensitivity to FCCP); at higher proline concentrations, a gradient-dependent mechanism became involved. Results with valinomycin indicated that proline-transport and oxidation are dependent upon the pH potential across the membrane, rather than the electrical (membrane) potential.