Restoration of Active Transport of Solutes and Oxidative Phosphorylation by Naphthoquinones in Irradiated Membrane Vesicles from Mycobacterium phlei

• Published in: Proceedings of the National Academy of Sciences - PNAS 1980-01, Vol.77 (1), p.102-106
• Main Authors: Lee, Soon-Ho, Sutherland, Thomas O., Deves, Rosa, Brodie, Arnold F.
• Format: Article
• Language: English
• Subjects: Active transport; Biological Sciences: Biochemistry; Biological Transport, Active - drug effects; Biological Transport, Active - radiation effects; Cell Membrane - radiation effects; Electrons; Light; Membrane potential; Membrane Potentials - drug effects; Membrane Potentials - radiation effects; Mycobacterium - metabolism; Mycobacterium phlei - metabolism; Mycobacterium phlei - radiation effects; Naphthoquinones; Naphthoquinones - pharmacology; Oxidation; Oxidative Phosphorylation - drug effects; Oxidative Phosphorylation - radiation effects; P branes; Phosphorylation; Protons; Quinones; Solutes; Uncoupling Agents - pharmacology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.77.1.102

Irradiation of the inverted membrane vesicles of Mycobacterium phlei with light at 360 nm inactivated the natural menaquinone [MK9(II-H)] and resulted in a loss of substrate oxidation, pH gradient, membrane potential, active transport of proline or calcium ions, and oxidative phosphorylation. Restoration of the protonmotive force and active transport occurred on addition of naphthoquinones such as vitamin K1, menadione, or lapachol to the irradiated membrane vesicles. However, coupled phosphorylation was restored only by vitamin K1. Menadione and lapachol did not act as uncoupling agents. The magnitude of the pH gradient and membrane potential in the quinone-restored system was a reflection of the rate of oxidation and was correlated with the rate of uptake of proline or Ca2+. These results are consistent with the chemosmotic hypothesis proposed for the energy transducing mechanism for active transport and further demonstrate that the complete respiratory chain is not required to drive active transport. In contrast, the data suggest that in addition to the driving force (protonmotive force) necessary to establish oxidative phosphorylation, a specific spatial orientation of the respiratory components, such as the naphthaquinones, is essential for the utilization of the proton gradient or membrane potential or both. Bypass of electrons from the respiratory chain with menadione may explain the inability of this quinone to restore oxidative phosphorylation; however, lapachol restores oxidation by the same electron transport pathway as the natural menaquinone but fails to restore phosphorylation. Because all three quinones restore the protonmotive force, other factors that are discussed must be considered in understanding the mechanism of oxidative phosphorylation.