גליקוליזה: שלב התשלום

Glycolysis is divided into two phases — the energy utilizing, preparatory phase and the energy releasing, pay-off phase.

The pay-off phase begins when 3-carbon G3P molecules are catabolized by the enzyme glyceraldehyde phosphate dehydrogenase to produce two molecules of 1,3-bisphosphoglycerate, simultaneously, producing two molecules of NADH.

Enzyme phosphoglycerate kinase then dephosphorylates 1,3-bisphosphoglycerate into two molecules of 3-phosphoglycerate while yielding two ATP molecules.

Thereafter, phosphoglycerate mutase converts 3-phosphoglycerate into 2-phosphoglycerate, which is further cleaved by enolase to produce two molecules of phosphoenolpyruvate or PEP.

Finally, another enzyme pyruvate kinase dephosphorylates PEP into pyruvate, yielding two more ATP molecules. Thus, the second phase of glycolysis produces four ATP and two NADH.

As two ATP are utilized during the first phase, the net results of glycolysis are two molecules, each of ATP, pyruvate, and NADH.