InterPro: IPR006424 Glyceraldehyde-3-phosphate dehydrogenase, type I

This group of sequences represent glyceraldehyde-3-phosphate dehydrogenase (GAPDH), the enzyme responsible for the interconversion of 1,3-diphosphoglycerate and glyceraldehyde-3-phosphate, a central step in glycolysis and gluconeogenesis. Forms exist which utilise NAD (EC:1.2.1.12), NADP (EC:1.2.1.13) or either (EC:1.2.1.59). In some species, NAD- and NADP- utilising forms exist, generally being responsible for reactions in the anabolic and catabolic directions respectively [1]. An additional form of gap gene is found in gamma proteobacteria and is responsible for the conversion of erythrose-4-phosphate (E4P) to 4-phospho-erythronate in the biosynthesis of pyridoxine [2]. This pathway of pyridoxine biosynthesis appears to be limited, however, to a relatively small number of bacterial species although it is prevalent among the gamma-proteobacteria [3]. This enzyme is described by IPR006422. These two groups of sequences exhibit a close evolutionary relationship. There exists the possibility that some forms of GAPDH may be bifunctional and act on E4P in species which make pyridoxine and via hydroxythreonine and lack a separate E4PDH enzyme (for instance, the GAPDH from Bacillus stearothermophilus has been shown to possess a limited E4PD activity as well as a robust GAPDH activity [4]).