The reaction mechanism of phosphomannomutase in plants

The enzyme phosphomannomutase catalyzes the interconversion of mannose-1-phosphate (Man-1-P) and mannose-6-phosphate (Man-6-P). In mammalian cells the enzyme has to be activated by transfer of a phosphate group from a sugar-1.6-P2 (Guha, S.K. and Rose, Z.B. (1985) Arch. Biochem. Biophys. 243, 168). In contrast, in the red alga Galdieria sulphuraria the co-substrate (Man-1.6-P2 or Glc-1.6-P2) is converted to the corresponding sugar monophosphate while the substrate is converted to the sugar bisphosphate in each reaction cycle. Evidence is presented that the same reaction mechanism occurs in spinach and yeast.