ENTPD1(Ectonucleoside triphosphate diphosphohydrolase 1) is also named as CD39, NTPDase 1, Ecto-ATPDase 1 and belongs to the GDA1/CD39 NTPase family. In the nervous system, it can hydrolyze ATP and other nucleotides to regulate purinergic neurotransmission.It is a noncovalent tetrameric protein and that detergent inhibition of enzymatic activity is caused by dissociation of ectoapyrase tetramers into monomers(PMID: 9733785).And it is a 70-to 100-kDa protein that is heavily N-glycosylated(PMID:7930580). It has 3 isoforms produced by alternative splicing. CD39 preferentially occurred as a dimer that could be dissociated into monomeric forms.(PMID: 12694193). The soluble isoform of CD39(38-478 amino acid) locates to the extracellular part and FNab01474 recognizes both the 3 isoforms and soluble form of CD39(38-478aa) molecule.