Involved in the synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions. In addition, may be responsible for the degradation of glucose-1,6-bisphosphate in ischemic brain. alpha-D-mannose 1-phosphate = D-mannose 6-phosphate IMP, a metabolite whose concentration is elevated in anoxia, inhibits phosphomannomutase and phosphoglucomutase activities and strongly enhances glucose-1,6-bisphosphatase activity. Nucleotide-sugar biosynthesis; GDP-alpha-D-mannose biosynthesis; alpha-D-mannose 1-phosphate from D-fructose 6-phosphate: step 2/2. Homodimer. Present in brain, where it is restricted to neuronal cell bodies. Present at lower levels in pancreas, liver, lung, gonads, uterus, adrenal glands and pituitary (at protein level). Undetectable in intestine. Highly expressed at 17 dpc in most organs (at protein level). Mice are viable and fertile and develop normally. Belongs to the eukaryotic PMM family.