<p>5'-nucleotidases <db_xref db="EC" dbkey="3.1.3.5"/> [<cite idref="PUB00000512"/>] are enzymes that catalyze the hydrolysis ofphosphate esterified at carbon 5' of the ribose and deoxyribose portions ofnucleotide molecules. 5'-nucleotidase is a ubiquitous enzyme found in a widevariety of species and which occurs in different cellular locations. The extracellular 5'-nucleotidase from mammals and <taxon tax_id="7785">Discopyge ommata</taxon> (Electric ray) isozyme is a homodimeric disulphide-bonded glycoprotein attached to the membrane by a GPI-anchor, and requires zinc for its activity. <taxon tax_id="670">Vibrio parahaemolyticus</taxon> 5'-nucleotidase (gene nutA) is bound to the membrane by a lipid chain, and requires chloride and magnesium ions for its activity. It is involved in degrading extracellular 5'-nucleotides for nutritional needs.</p><p> Periplasmic bacterial 5'-nucleotidase (gene ushA), also known as UDP-sugar hydrolase <db_xref db="EC" dbkey="3.6.1.45"/>, can degrade UDP-glucose and other nucleotide diphosphate sugars. It produces sugar-1-phosphate which can then be used by the cell. UshA seems to require cobalt for its activity.5'-Nucleotidases are evolutionary related to the periplasmic bacterial 2',3'-cyclic-nucleotide 2'-phosphodiesterase <db_xref db="EC" dbkey="3.1.4.16"/> (gene cpdB), which catalyzes two consecutive reactions: it first converts 2',3'-cyclic-nucleotide to 3'-nucleotide and then acts as a 3'-nucleotidase; and mosquito apyrase <db_xref db="EC" dbkey="3.6.1.5"/> (ATP-diphosphohydrolase) [<cite idref="PUB00004869"/>], which catalyzes the hydrolysis of ATP into AMP and facilitates hematophagy by preventing ADP-dependent platelet aggregation in the host.</p><p>CD73 (also called ecto-5'-nucleotidase) possesses the enzymatic activity of a 5'-nucleotidase and catalyses the dephosphorylation of purine and pyrimidine ribo- and deoxyribonucleoside monophosphates to their corresponding nucleosides. Triggering of lymphocyte CD73 with mAb causes phosphorylation and dephosphorylation of certain, yet unknown protein substrates [<cite idref="PUB00008988"/>]. A possible function for CD73 is to regulate the availability of adenosine for interaction with cell surface adenosine receptor by converting AMP to adenosine. In common with other GPI anchored surface proteins CD73 can mediate costimulatory signals in T cell activation [<cite idref="PUB00008989"/>].</p><p>CD molecules are leucocyte antigens on cell surfaces. CD antigens nomenclature is updated at Protein Reviews On The Web (http://prow.nci.nih.gov/).</p>