<p>This family of sequences represent 2-phosphoglycolate phosphatase which is limited to the eukaryotic lineage. PGP is an essential enzyme in the glycolate salvage pathway in higher organisms (photorespiration in plants). Phosphoglycolate results from the oxidase activity of RubisCO in the Calvin cycle when concentrations of carbon dioxide are low relative to oxygen. In mammals, PGP is found in many tissues, notably in red blood cells where P-glycolate is and important activator of the hydrolysis of 2,3-bisphosphoglycerate, a major modifier of the oxygen affinity of hemoglobin. The PGPase enzyme described here is a member of the Haloacid dehalogenase superfamily of hydrolase enzymes. Unlike the bacterial PGP equivalog (<db_xref db="INTERPRO" dbkey="IPR006346"/>), which is a member of class (subfamily) I, this enzyme is a member of class (subfamily) II [<cite idref="PUB00009589"/>]. These two enzymes have almost certainly arisen from convergent evolution (although these two ancestors may themselves have diverged from a more distant HAD superfamily progenitor). One of the sequences in the group comes from <taxon tax_id="3055">Chlamydomonas reinhardtii</taxon>, a photosynthetic alga. The enzyme has been purified and characterised and these data are fully consistent with the assignment of function as a PGPase involved in photorespiration [<cite idref="PUB00009590"/>]. Another, from <taxon tax_id="9606">Homo sapiens</taxon> (Human), is supported as a member of the family indirectly. Biochemical characterisation of partially purified PGP's from various tissues including red blood cells [<cite idref="PUB00009591"/>] have been performed while one gene for PGP has been localized to chromosome 16p13.3 [<cite idref="PUB00009592"/>]. The <taxon tax_id="9606">Homo sapiens</taxon> (Human) sequence maps to chromosome 22. There is indeed a related gene on chromosome 16 (and it is expressed, since EST's are found) which shows 46% identity and 59% positives by BLAST2 (E=1e-66). Presumably, these two genes are isoforms and have the same catalytic function while being expressed in different tissues and may be differently regulated. The sequence from <taxon tax_id="6239">Caenorhabditis elegans</taxon>, is only supported by sequence similarity. This family is closely related to a family of bacterial sequences including the <taxon tax_id="562">Escherichia coli</taxon> NagD and <taxon tax_id="1423">Bacillus subtilis</taxon> AraL genes which are characterised by the ability to hydrolyze para-nitrophenylphosphate (pNPPases or NPPases). The <taxon tax_id="3055">Chlamydomonas reinhardtii</taxon> PGPase does not catalyze this reaction and so presumably these two groups have different functions and substrate specificities. Many of the genes in this family have been annotated as pNPPases due to this association.</p>