Glycolysis is the lysis, or splitting, of one molecule of glucose into two molecules of pyruvate, producing a net gain of two ATP molecules. Pyruvate can then be used in anaerobic (fermentation) or aerobic (respiration) metabolism. The glycolysis pathway and the genes involved are illustrated here.

During glycolysis, Pgk1p (3-phosphoglycerate kinase) catalyzes the transfer of a high-energy phosphoryl group from the acyl phosphate of 1,3-diphosphoglycerate to ADP to produce ATP. Pgk1p also catalyzes the reverse reaction during gluconeogenesis wherein 3-phosphoglycerate and ATP are converted to 1,3-diphosphoglycerate and ADP (2, 3). The reversible reaction is catalyzed in the presence of magnesium ions.

Gluconeogenesis is the process whereby glucose is synthesized from non-carbohydrate precursors, which enables yeast cells to grow on non-sugar carbon sources like ethanol, glycerol, or peptone. The reactions of gluconeogenesis, shown here, mediate conversion of pyruvate to glucose, which is the opposite of glycolysis, the formation of pyruvate from glucose. While these two pathways have several reactions in common, they are not the exact reverse of each other. As the glycolytic enzymes phosphofructokinase (Pfk1p, Pfk2p) and pyruvate kinase (Cdc19p) only function in the forward direction, the gluconeogenesis pathway replaces those steps with the enzymes pyruvate carboxylase (Pyc1p, Pyc2p) and phosphoenolpyruvate carboxykinase (Pck1p)-generating oxaloacetate as an intermediate from pyruvate to phosphoenolpyruvate-and also the enzyme fructose-1,6-bisphosphatase (Fbp1p) (reviewed in 4). Overall, the gluconeogenic reactions convert two molecules of pyruvate to a molecule of glucose, with the expenditure of six high-energy phosphate bonds, four from ATP and two from GTP.

Pgk1p is composed of two structurally similar domains linked by a helical hinge that also interact through a C-terminal helix (5). Purification of Pgk1p from a variety of organisms indicates that it has been highly conserved throughout evolution (6).

PGK1 is abundantly expressed in cells growing in glucose, and transcription is increased by heat shock (7). In contrast, mRNA levels are low in cells grown in pyruvate, acetate, or lactate, although the message stability is not affected by the carbon source (8, 9). Transcription is activated by the transcription factors Rap1p, Abf1p, and Reb1p, which each bind to sequences in the PGK1 promoter (8, 10). Because PGK1 is a highly-expressed gene and its mRNA is relatively stable, it has been the subject of a large number of studies on mRNA stability and decay, codon bias, and protein structure, folding, and kinetics (see Literature Guide for a complete listing).

Last updated: 2005-07-22