Coupling/Uncoupling Reversibility in Isolated Mitochondria from Saccharomyces cerevisiae

Lilia Morales-García,Salvador Uribe-Carvajal,Natalia Chiquete-Félix,Carolina Ricardez-García,Paulina Castañeda-Tamez

doi:10.3390/life11121307

Lilia Morales-García, Salvador Uribe-Carvajal + Show 3 more

Open Access

https://doi.org/10.3390/life11121307

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Abstract

The yeast Saccharomyces cerevisiae uses fermentation as the preferred pathway to obtain ATP and requires the respiratory chain to re-oxidize the NADH needed for activity of Glyceraldehyde-3-phosphate. This process is favored by uncoupling of oxidative phosphorylation (OxPhos), which is at least partially controlled by the mitochondrial unspecific pore (ScMUC). When mitochondrial ATP synthesis is needed as in the diauxic phase or during mating, a large rise in Ca2+ concentration ([Ca2+]) closes ScMUC, coupling OxPhos. In addition, ScMUC opening/closing is mediated by the ATP/ADP ratio, which indicates cellular energy needs. Here, opening and closing of ScMUC was evaluated in isolated mitochondria from S. cerevisiae at different incubation times and in the presence of different ATP/ADP ratios or varying [Ca2+]. Measurements of the rate of O2 consumption, mitochondrial swelling, transmembrane potential and ROS generation were conducted. It was observed that ScMUC opening was reversible, a high ATP/ADP ratio promoted opening and [Ca2+] closed ScMUC even after several minutes of incubation in the open state. In the absence of ATP synthesis, closure of ScMUC resulted in an increase in ROS.

Highlights

Fermentative metabolism in Saccharomyces cerevisiae requires an active mitochondrial respiratory chain to re-oxidize the NADH produced by glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [1]
NAD+ is needed in the glycolytic pathway by glyceraldehyde-3Phosphate dehydrogenase (GAPDH), which may bind to mitochondrial porin and exchange produced NADH for required NAD+ [2]
A high ∆Ψ would inhibit the rate of oxygen consumption by the respiratory chain (RC) [1], RC does work at a high rate in order to oxidize NADH and produce the NAD+ needed for glyceraldehyde-3-phosphate dehydrogenase activity [29]

Summary

Introduction

Fermentative metabolism in Saccharomyces cerevisiae requires an active mitochondrial respiratory chain to re-oxidize the NADH produced by glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [1]. The S. cerevisiae mitochondrial unspecific channel (ScMUC) may open, depleting the transmembrane potential (∆Ψ), uncoupling oxidative phosphorylation and increasing the rate of oxygen consumption, decreasing ROS production further [5,6,7]. An a-cell and an α-cell undergo fusion to generate a diploid [15] As these processes require a large amount of energy, Ca2+ is needed to close ScMUC, promote OxPhos coupling and increase ATP availability. In addition it was observed that opening was gradual as effector mixtures elicited partial effects These effects suggest that in fermenting yeast, mitochondria are uncoupled, becoming coupled when a large amount of ATP is required

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