On the basis of what has been reported in this review article, we can affirm that the AP activity is the result of various enzymes which display different molecular and biochemical properties, are localized in different cell compartments and perhaps into different discrete cytoplasmic domains. These findings are consistent with the distinct physiological role of each AP form. The enzymes are present in tissue of all vertebrates at various evolutionary levels indicating a great importance in cell physiology and their early sorting among vertebrate cell metabolism. The amino acid sequence homology and immunological similarity between some enzymes suggest that they arise from common ancestor molecules. The extension of AP studies to chordate level could be useful for understanding this hypothesis. As reported for other protein molecules the APs seems to be to belong to a multigene family. The reason for enzyme sorting from a cell type is not yet known and will be the object of further studies as well as the enzyme structure and regulation of gene expression mechanisms not only in adults but also during embryonic animal development. The observation that some AP forms actively dephosphorylate P-Tyr containing proteins is of interest and indicates that these enzymes can be involved in the control of cell proliferation and transformation.
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