<p>This enzyme is known to be bifunctional, as both mannose-6-phosphate isomerase (<db_xref db="EC" dbkey="5.3.1.8"/>) (PMI) and mannose-1-phosphate guanylyltransferase (<db_xref db="EC" dbkey="2.7.7.22"/>) in <taxon tax_id="287">Pseudomonas aeruginosa</taxon>, <taxon tax_id="339">Xanthomonas campestris</taxon>, and <taxon tax_id="28448">Acetobacter xylinus</taxon>. The literature on the enzyme from <taxon tax_id="562">Escherichia coli</taxon> attributes mannose-6-phosphate isomerase activity to an adjacent gene, but the present sequence has not been shown to lack the activity. The PMI domain lies at the C-terminal. </p><p>Mannose-6-phosphate isomerase or phosphomannose isomerase (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>