COMPARISON OF PMM1 WITH THE PHOSPHOMANNOMUTASES EXPRESSED IN RAT-LIVER AND IN HUMAN-CELLS

Carbohydrate-deficient glycoprotein syndrome type I (CDGI) is most oft en due to phosphomannomutase deficiency; paradoxically, the human phos phomannomutase gene PMM1 is located on chromosome 22, whereas the CDGI locus is on chromosome 16, We show that phosphomannomutases present i n rat or human liver share with homogeneous recombinant PMM1 several k inetic properties and the ability to form an alkali- and NH2OH-sensiti ve phosphoenzyme with a subunit mass of approximate to 30 000 M-r. How ever, they have a higher affinity for the activator mannose-1,6-bispho sphate than PMM1 and are not recognized by anti-PMM1 antibodies, indic ating that they represent a related but different isozyme, Phosphomann omutases belong to a novel mutase family in which the active residue i s a phosphoaspartyl or a phosphoglutamyl. (C) 1997 Federation of Europ ean Biochemical Societies.