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. Strong expression in liver, heart, brain, and pancreas; lower expression in skeletal muscle. Belongs to the eukaryotic PMM family.