Inositol monophosphatase is a highly conserved enzyme having localized structural similarity to both glycerol...

The cDNA coding for an inositol monophosphatase in the oocytes of the African clawed frog, Xenopus laevis, has been isolated and sequenced. The predicted primary structure of this enzyme is markedly conserved when it is compared with its mammalian functional homologues; up to 84% of the amino acid residues are identical, and conservative substitutions increase the similarity to 95%, suggesting that this sequence represents the most parsimonious primary structure for the protein to maintain not only catalytic activity but also perhaps the facility to interact with other macromolecules. Two regions of the protein, each of about 11 residues and separated by about 90 residues, have been identified as a consensus found also in glycerol 3-phosphate dehydrogenase (EC 1.1.1.8). One of these regions is also found to be particularly conserved in the alpha-globin of birds and reptiles; birds and some turtles are known to modulate the oxygen affinity of their haemoglobin with inositol polyphosphate in the same way as with 2,3-bisphosphoglycerate in other species. This region is also conserved in the beta-globin of most species, beginning with lysine-82, which is known to participate in the binding of organic phosphates. These regions of the inositol monophosphatase may represent motifs for the binding of its substrate.