Glyceraldehyde-3-phosphate dehydrogenase, type I <p>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 (<db_xref db="EC" dbkey="1.2.1.12"/>), NADP (<db_xref db="EC" dbkey="1.2.1.13"/>) or either (<db_xref db="EC" dbkey="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 [<cite idref="PUB00009631"/>]. 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 [<cite idref="PUB00002270"/>]. 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 [<cite idref="PUB00009725"/>]. This enzyme is described by <db_xref db="INTERPRO" dbkey="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 <taxon tax_id="1422">Bacillus stearothermophilus</taxon> has been shown to possess a limited E4PD activity as well as a robust GAPDH activity [<cite idref="PUB00009726"/>]).</p>