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A glucose-activated electron transfer system in the plasma membrane stimulates the H(+)-ATPase in Penicillium
1Abteilung Biotechnologie/Zellphysiologie, Martin-Luther-Universität, Halle (Saale), Germany.
Abstract:
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.
Insights
Fungal cells, specifically Penicillium cyclopium, can reduce external electron acceptors like hexabromoiridate IV (HBI IV). Beta-glucose significantly enhances this process, suggesting a direct interaction with a cell surface component.
Area of Science:
- Mycology
- Biochemistry
- Cell Biology
Background:
- Fungal hyphal cells possess mechanisms for extracellular electron transfer.
- The genus Penicillium includes species with potential roles in redox reactions.
Purpose of the Study:
- To investigate the reduction of hexabromoiridate IV (HBI IV) by Penicillium species.
- To determine the effect of beta-glucose on HBI IV reduction.
- To elucidate the underlying mechanisms of trans-plasma membrane electron transport.
Main Methods:
- Incubation of Penicillium hyphal cells with HBI IV.
- Addition of beta-glucose and other sugars to assess specificity.
- Measurement of H2O2 production and oxygen dependence.
- Confocal pH topography to monitor intracellular and extracellular pH changes.
- Use of plasma membrane vesicles and a membrane potential-sensitive fluoroprobe (Di-8-ANEPPS).
- Application of inhibitors of proton pumping.
Main Results:
- Penicillium hyphal cells reduced HBI IV, with Penicillium cyclopium showing a significant increase upon beta-glucose addition.
- The stimulatory effect of beta-glucose was specific and did not require cellular uptake or metabolism.
- No H2O2 was detected, and oxygen removal had no effect, suggesting oxidases were not involved.
- HBI IV reduction led to intracellular acidification and subsequent extracellular acidification with a high e-/H+ stoichiometry.
- The external electron acceptor induced membrane depolarization in plasma membrane vesicles.
- Inhibition of proton pumps enhanced depolarization and reduced proton extrusion.
Conclusions:
- A specific, external glucose-binding component likely controls transmembrane electron fluxes in Penicillium.
- The trans-plasma membrane redox process activates the H(+)-ATPase through membrane depolarization and cytosolic acidification.