Active Transport of Proline in Membrane Preparations from Mycobacterium phlei

Active transport of proline was observed in both electron transport particles and cell membrane ghosts from Mycobacterium phlei. The transport of proline was dependent upon substrate oxidation and the presence of Li+ or Na+, but not upon the formation of a high energy phosphorylated intermediate. The requirement for Na+ was different from Na+ coupled transport systems which have been described; as the concentration of Na+ was increased, the Vmax of proline transport increased while the Km remained constant. Sonication of the membrane ghost preparations resulted in membrane vesicles which were equivalent to electron transport particles with respect to membrane orientation, and which were able to actively transport proline. The transport of proline by either of the two membrane preparations was dependent upon the nature of the substrate used as electron donor. Ascorbate-tetramethyl-p-phenylenediamine or succinate supported the transport of proline equally well in the membrane ghost preparations. In contrast, the transport of proline with electron transport particles was 10-fold greater with ascorbate-tetramethyl-p-phenylenediamine than with succinate. Furthermore, succinate induced proline efflux with the electron transport particles, but not with the membrane ghost preparations. Evidence is presented that succinic dehydrogenase is located on the cytoplasmic side of the membrane.