Yeast Aconitase in Two Locations and Two Metabolic Pathways: Seeing Small Amounts is Believing.
Neta Regev-Rudzki, Sharon Karniely, Ophry Pines
Department Molecular Biology, Hebrew University of Jerusalem, Ein-Karem, Jerusalem, 91120, Israel
The distribution of identical enzymatic activities between different subcellular compartments is a fundamental process of living cells. We maintain that such a distribution phenomenon has a wider occurrence than recorded currently; the reason being that in certain cases there is a small fraction of one of the isoenzymes, in one of the locations, making its detection very difficult. We term this phenomenon 'eclipsed distribution'. At present the Saccharomyces cerevisiae aconitase enzyme has been detected only in mitochondria, where it functions in the tricarboxylic acid (TCA) cycle and is considered a mitochondrial matrix marker. We developed two strategies for physical and functional detection of aconitase in the yeast cytosol: 1) We fused the a peptide of the β-galactosidase enzyme to aconitase and observed a complementation in the cytosol. 2) We created an ACO1-URA3 hybrid gene, which allowed isolation of strains in which the hybrid protein is exclusively targeted to mitochondria. These strains display a specific phenotype consistent with glyoxylate shunt elimination. Together, our data indicate that yeast aconitase isoenzymes distribute between two distinct subcellular compartments and participate in two separate metabolic pathways; the glyoxylate shunt in the cytosol and the TCA cycle in mitochondria.