Identification of the nucleotidase responsible for the AMP hydrolysing hyperactivity associated with neurological and developmental disorders.

Nucleoside monophosphate phosphohydrolases comprise a family of enzymes dephosphorylating nucleotides both in intracellular and extracellular compartments. Members of this family exhibit different sequence, location, substrate specificity and regulation. Besides the ectosolic 5'-nucleotidase, several cytosolic and one mitochondrial enzymes have been described. Nevertheless, researchers refer any AMP-dephosphorylating activity to as 5'-nucleotidase, lacking a more accurate identification. Increase of AMP hydrolysing activity has been associated with neurological and developmental disorders. The identification of the specific enzyme involved in these pathologies would be fundamental for the comprehension of the linkage between the enzyme activity alteration and brain functions. We demonstrate that the described neurological symptoms are associated with increased ectosolic 5'-nucleotidase activity on the basis of radiochemical assays and immunoblotting analysis. Furthermore, present data evidence that the assay conditions normally applied for the determination of cytosolic 5'-nucleotidases activity in crude extracts are affected by the presence of solubilised ectosolic nucleotidase.