Glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde 3-phosphate dehydrogenase (abbreviated GAPDH) () is an enzyme of about 37kDa that catalyzes the sixth step of glycolysis and thus serves to break down glucose for energy and carbon molecules. In addition to this long established metabolic function, GAPDH has recently been implicated in several non-metabolic processes, including transcription activation, initiation of apoptosis, ER to Golgi vesicle shuttling, and fast axonal, or axoplasmic transport. In sperm, a testis-specific isoenzyme GAPDHS is expressed. Structure Under normal cellular conditions, cytoplasmic GAPDH exists primarily as a tetramer. This form is composed of four identical 37-kDa subunits containing a single catalytic thiol group each and critical to the enzyme's catalytic function. Nuclear GAPDH has increased isoelectric point (pI) of pH 8.3–8.7. Of note, the cysteine residue C152 in the enzyme's active site is required for the induction of apoptosis by oxidative stress. Notably, post-translational modifications of cytoplasmic GAPDH contribute to its functions outside of glycolysis. GAPDH is encoded by a single gene that produces a single mRNA transcript with 8 splice variants, though an isoform does exist as a separate gene that is expressed only in spermatozoa.