Mannose Phosphate Isomerase (MPI)

Phosphomannose isomerase catalyzes the interconversion of fructose-6-phosphate and mannose-6-phosphate and plays a critical role in maintaining the supply of D-mannose derivatives, which are required for most glycosylation reactions. Mutations in the MPI gene were found in patients with carbohydrate-deficient glycoprotein syndrome, type Ib. The authors used sequence information obtained from internal fragments of the protein to design degenerate oligonucleotides which were used to amplify a fragment of the PMI cDNA.The PMI gene encodes a predicted 423-amino acid polypeptide. Northern blot analysis detected a single 1.8-kb PMI mRNA in all tissues tested, with the highest levels in heart, brain, and skeletal muscle. Recombinant PMI expressed in E. coli had very similar activity to the native enzyme.