Prodigiosins As a New Group of H+/Cl- Symporters That Uncouple Proton Translocators

We reported previously (Kataoka, T., Muroi, M., Ohkuma, S., Waritani, T., Magae, J., Takatsuki, A., Kondo, S., Yamasaki, M., and Nagai, K. (1995) FEBS Lett. 359, 53-59) that prodigiosin 25-C uncoupled vacuolar H+-ATPase, inhibited vacuolar acidification, and affected glycoprotein processing. In the present study we show that prodigiosins (prodigiosin, metacycloprodigiosin, and prodigiosin 25-C) inhibit the acidification activity of H+-ATPase chloride dependently, but not membrane potential formation or ATP hydrolysis activity, and suggest that they promote H+/Cl- symport (or OH-/Cl- exchange, in its equivalence) across vesicular membranes. In fact, prodigiosins displayed H+/Cl- symport activity on liposomal membranes. First of all, they decreased the internal pH of liposomes depending on the external chloride, and raised it depending on the internal chloride when external buffer was free from chloride. Second, their effect was electroneutral and not seriously affected by the application of an inside positive membrane potential generated by K+ and valinomycin. Finally, they promoted the uptake of [36Cl] from external buffers with concomitant intraliposomal acidification when external pH was acidic relative to liposome interior. As prodigiosins hardly inhibit the catalytic activity (ATP hydrolysis) unlike well known OH-/Cl- exchangers (for example, tributyltin chloride), they should provide powerful tools for the study of molecular machinery and cellular activities involving transport of protons and/or chloride.