the hemithioacetal is oxidized to a thioester. This thioester species is much higher in energy (less stable) than the carboxylic acid species that would result if GAP were oxidized in the absence of GAPDH (the carboxylic acid species is so low in energy that the energy barrier for the second step of the reaction (phosphorylation) would be too high, and the reaction, therefore, too slow and unfavorable for a living organism). 2: Phosphorylation NADH leaves the active site and is replaced by another molecule of NAD+, the positive charge of which stabilizes the negatively charged carbonyl oxygen in the transition state of the next and ultimate step. Finally, a molecule of inorganic phosphate attacks the thioester and forms a tetrahedral intermediate, which then collapses to release 1,3-bisphosphoglycerate, and the thiol group of the enzyme's cysteine residue. Regulation This protein may use the morpheein model of allosteric regulation. Function Metabolic As its name indicates, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyses the conversion of glyceraldehyde 3-phosphate to D-glycerate 1,3-bisphosphate. This is the 6th step in the glycolytic breakdown of glucose, an important pathway of energy and carbon molecule supply which takes place in the cytosol of eukaryotic cells. The conversion occurs in two coupled steps. The first is favourable and allows the second unfavourable step to occur. Adhesion One of the GAPDH moonlighting function is its role in adhesion and binding to other partners. Bacterial GAPDH from Mycoplasma and Streptococcus and fungal GAPDH from Paracoccidioides brasiliensis are known to bind with the human extracellular matrix component and act in adhesion. GAPDH is found to be surface bound contributing in adhesion and also in competitve exclusion of harmful pathogens. GAPDH from Candida albicans is found to cell-wall associated and binds to Fibronectin and Laminin. GAPDH from probiotics species are known to bind human colonic mucin and ECM, resulting in enhanced colonization of probiotics in the human gut. Patel D. et al., showed that Lactobacillus acidophilus GAPDH binds with mucin, acting in adhesion. Transcription and apoptosis GAPDH can itself activate transcription. The OCA-S transcriptional coactivator complex contains GAPDH and lactate dehydrogenase, two proteins previously only thought to be involved in metabolism. GAPDH moves between the cytosol and the nucleus and may thus link the metabolic state to gene transcription. In 2005, Hara et al. showed that GAPDH initiates apoptosis. This is not a third function, but can be seen as an activity mediated by GAPDH