<p>Mannose-6-phosphate isomerase or phosphomannose isomerase (<db_xref db="EC" dbkey="5.3.1.8"/>) (PMI) is the enzyme that catalyses the interconversion of mannose-6-phosphate and fructose-6-phosphate. In eukaryotes PMI is involved in the synthesis of GDP-mannose, a constituent of N- and O-linked glycans and GPI anchors and in prokaryotes it participates in a variety of pathways, including capsular polysaccharide biosynthesis and D-mannose metabolism. PMI's belong to the cupin superfamily whose functions range from isomerase and epimerase activities involved in the modification of cell wall carbohydrates in bacteria and plants, to non-enzymatic storage proteins in plant seeds, and transcription factors linked to congenital baldness in mammals [<cite idref="PUB00007419"/>]. Three classes of PMI have been defined [<cite idref="PUB00001448"/>].</p>The type II phosphomannose isomerases are bifunctional enzymes <db_xref db="EC" dbkey="5.3.1.8"/>. This entry covers the isomerase region of the protein [<cite idref="PUB00000676"/>]. The guanosine diphospho-D-mannose pyrophosphorylase region is described in another InterPro entry (see <db_xref db="INTERPRO" dbkey="IPR005836"/>).