A study on the mechanism of siderophore transport ‐ a proton symport

Abstract

The mechanism of siderophore transport in fungi was studied with cells of Neurospora crassa using [⁵⁵Fe]‐ferricrocin as a siderophore. In the presence of respiratory inhibitors and uncouplers transport of siderophores is immediately inhibited. Measurements of the ATP content of the cells revealed different levels of ATP, depending on the concentration of inhibitors and the time of incubation, Thus, transport inhibition is not a result of decreased ATP level, but rather due to the concomitant membrane depolarization. To study the role of the membrane potential for siderophore iron transport, glu‐II derepressed cells were used, which show membrane depolarization after the addition of high amounts of glucose, without ATP depletion. During depolarization siderophore iron transport was inhibited for a short time, followed by a recovering phase. Inhibition of the membrane ATP‐ase by N ,N'‐dicyclohexyl carbodiimide (DCCD) or diethylstilbestrol (DES) during membrane depolarization prevented the regeneration of the membrane potential, resulting in a long lasting inhibition of siderophore uptake. These results strongly suggest that the membrane potential of the plasma membrane is essential for siderophore uptake in fungi and that siderophores are translocated by a proton symport.

Key words:

• Ferricrocin
• Membrane potential
• proton symport