A glucose-activated electron transfer system in the plasma membrane stimulates the H(+)-ATPase in Penicillium cyclopium.

Hyphal cells of three fungal species of the genus Penicillium reduced the nonpermeable, external electron acceptor hexabromoiridate IV (HBI IV). In Penicillium cyclopium, the rate of HBI IV reduction by hyphal cells was drastically increased by the addition of beta-glucose. The stimulation showed high specificity for this sugar and did not require its uptake and cellular metabolism. Cell wall oxidases (e.g., glucose oxidase) did not seem to be involved in the reduction of HBI IV, as no measurable H2O2 was formed from added glucose and removal of oxygen had no effect. We propose that there is a glucose-binding component outside the plasma membrane which controls transmembrane electron fluxes in response to external glucose. Reduction of HBI IV was accompanied by rapid acidification of the cellular interior (measured by confocal pH topography). Subsequently, the outer medium was acidified of the cellular interior (measured by confocal pH topography). Subsequently, the outer medium was acidified with an e-/H+ stoichiometry of > 1. In plasma membrane vesicles containing endogenous electron donors, the membrane-residing fluoroprobe Di-8-ANEPPS reported a transient depolarization of the membrane potential triggered by the external electron acceptor. Inhibitors of ATP-dependent proton pumping enhanced the extent of this depolarization, inhibited the subsequent normalization of membrane potential, and, in whole cells, reduced the amount of redox-triggered proton extrusion. From these and other findings, it is concluded that the observed trans-plasma membrane redox process activates the H(+)-ATPase via membrane depolarization and cytosolic acidification.