Basic biology of GAPDH.

The GAPDH gene is highly conserved with a promoter that contains several types of regulatory elements, perhaps even in a distal intron. Curiously, the transcription start site shows some ambiguity and there are codon-sharing exons at alternate exon junctions. While there is only one functional gene for GAPDH in humans, the genome is littered with pseudogenes, representing a trove of researchable content. Tissue-specific expression speaks to the glycolytic function of GAPDH; thus, it's not surprising to see expression increased in cancer cells. Modulation of protein levels becomes an opportunity for intervention. The abundance of GAPDH in the cell provides the rationale (albeit, tenuous) for its use as a loading control. The single paralogous GAPDHS, which is the spermatogenic form of the protein, provides a curious study in cell-type specificity and perhaps intervention (i.e. contraception). And it is no wonder that great biochemists were kept busy for decades unveiling the nuances of GAPDH enzymology. While the active site of the enzyme is well-characterized and the catalytic mechanism is well-described, the role of inter-subunit interactions in catalysis still offers some mysteries, particularly with regards to other emerging enzymatic properties. The GAPDH protein exhibits an intrinsic asymmetry of the subunits, which also may speak to its functional diversity.