Studies on the Regulation and Localization of the Glyoxylate Cycle Enzymes in Saccharomyces cerevisiae

Abstract

The regulation of the enzymes involved in the operation of the glyoxylate cycle was studied in the yeast Saccharomyces cerevisiae. All enzymes showed an increase in specific activity under growth conditions where the glyoxylate cycle is needed as an anaplerotic pathway. I n the presence of 1 Olio glucose, t,he synthesis of all enzymes, except fumarase, was repressed. However, no indication for a specific regulation mechanism for the entire cycle could be found.Studies on the localization of the glyoxylate cycle enzymes in the yeast cell revealed that the key enzymes, isocitrate lyase and malate synthase, are located in the cytoplasm, whereas succinate dehydrogenase was found only in the mitochondria1 fraction. Activities of all other enzymes are found in the cytoplasm as well as in the mitochondria. I n anaerobically grown cells, no mitochondria could be detected. Succinate dehydrogenase, isocitrate lyase, and malate synthase were absent. However, appreciable activities of citrate synthase, aconitase, fumarase, and malate dehydrogenase were found in the cytoplasm.The significance of these observations for the operation of the glyoxylate cycle is discussed.The ability of many microorganisms, including the yeast Saccharomyces cerevisiae, to grow on 2-carbon compounds such as acetate or ethanol as the only carbon source, is linked to the anaplerotic function of the glyoxylate cycle. As the net result of one turn of this cycle two molecules of acetyl-coenzyme A are combined into one molecule of succinate, which can serve as a precursor for gluconeogenesis [I]. As it was first shown by Kornberg [2], the activities of the key enzymes of the cycle, isocitrate lyase and malate synthase, are regulated in yeast in response to the carbon source of the growth medium. The synthesis of each of these enzymes is repressed in cells grown on glucose and derepressed in glucose-free media [3,4] or after the glucose in the medium has been exhausted [3,6]. Malate dehydrogenase is regulated in a similar way [3,4,6]. Moreover, several isoenzymes of malate dehydrogenase, of which only one exhibits this type of regulation, have been found in yeast [5,7]. This isoenzyme is located in the cytoplasm and seems to be specifically involved in the functioning of the glyoxylate cycle. (EC 1.3.99.1). B* I n the experiments described here, we studied the regulation of other enzymes of the glyoxylate cycle under the influence of the carbon source of the medium. Since the operation of the glyoxylate cycle requires several enzymatic steps that are also involved in the citric acid cycle, we were especially interested in whether the glyoxylate cycle in yeast is regulated and operates as a functional unit independently from the citric acid cycle. As in other organisms, the citric acid cycle of yeast is located in the mitochondria [8,9]. Therefore, the demonstration by Witt et al. [5] of a cytoplasmic isoenzyme of malate dehydrogenase, probably specific for the glyoxylate cycle, indicated a possible spatial separation of the two pathways. To obtain i...

Horizontal gene transfer promoted evolution of the ability to propagate under anaerobic conditions in yeasts

“…Nevertheless, it is apparent that, while SkmtDHODase is likely to be dependent on electron acceptors which require the integrity of the respiratory chain, SkcytDHODase can catalyse the transfer of electrons to a larger variety of acceptors, including fumarate. The presence of fumarate in the yeast cell is independent of a functional respiratory chain, since it can be generated in the cytoplasm via the glyoxylate cycle (Duntze et al 1969;Gancedo and Serrano 1989).…”

Phosphoenolpyruvate Carboxykinase as the Sole Anaplerotic Enzyme in Saccharomyces cerevisiae

“…This multilayered regulation has presumably evolved to avoid futile cycling due to simultaneous decarboxylating PEPCK and carboxylating pyruvate carboxylase activities. In line with this, the central enzymes in the glyoxylate cycle, another anaplerotic alternative to pyruvate carboxylase, are also repressed by glucose (16,17,20,32). As a consequence, S. cerevisiae strains lacking the PYC1 and PYC2 genes, encoding the pyruvate carboxylase isoenzymes, are unable to fulfill their anaplerotic requirements during growth on glucose and are auxotrophic for 4-carbon molecules, such as aspartate (34).…”

“…The absence of glyoxylate cycle derepression mutants during selection might be explained by inhibition of succinate dehydrogenase by CO 2 (4,15,40). As this enzyme is required for a functional glyoxylate cycle, its inhibition by CO 2 would represent a second hurdle in addition to the glucose repression of the glyoxylate cycle enzymes isocitrate lyase and malate synthase (16,17,20,32).…”

Contribution of the tricarboxylic acid (TCA) cycle and the glyoxylate shunt in Saccharomyces cerevisiae to succinic acid production during dough fermentation

“…The ACO1 mutant is not able to convert citrate to isocitrate which is a substrate for both isocitrate lyase and isocitrate dehydrogenase. The presence of yeast aconitase in the cytosol and mitochondria demonstrates that it participates in the glyoxylate shunt and the TCA cycle, respectively (Dduntze et al, 1969;Gangloff et al, 1990;Regev-Rudzki et al, 2005).…”

“…The glyoxylate shunt is located in the cytoplasm. The key enzymes of this shunt, isocitrate lyase and malate synthase, are strongly repressed in cells growing on high glucose concentration (Chapman and Bartley, 1968;Dduntze et al, 1969;Magarifuchi et al, 1995). Deletion of ICL1 resulted in the absence of isocitrate lyase activity and the lack of the ability of yeast to grow on ethanol as the sole carbon source (Fernandez et al, 1992;Heinisch et al, 1996;Luttik et al, 2000).…”