CD39-L4 is a secreted human apyrase, specific for the hydrolysis of nucleoside diphosphates.
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Mulero JJ, Yeung G, Nelken ST, Ford JE
CD39-L4 is a secreted human apyrase, specific for the hydrolysis of nucleoside diphosphates.
J Biol Chem. 1999 Jul 16;274(29):20064-7. doi: 10.1074/jbc.274.29.20064.
- PubMed ID
- 10400613 [ View in PubMed]
- Abstract
The human ecto-apyrase gene family consists of five reported members (CD39, CD39-L1, CD39-L2, CD39-L3, and CD39-L4). The family can be subdivided into two groups by conservation of proposed structural domains. The CD39, CD39-L1, and CD39-L3 genes all encode hydrophobic portions in their carboxy and amino termini, serving as transmembrane domains for CD39 and potentially for the other two members. CD39-L2 and CD39-L4 genes encode hydrophobic portions in their amino termini, suggesting that they might encode secreted apyrases. We demonstrate that the CD39-L4 gene encodes the first reported human secreted ecto-apyrase. COS-7 cells transfected with a CD39-L4 expression construct utilizing the naturally occurring leader peptide express recombinant protein outside of the cells. This expression can be blocked by brefeldin A, a chemical that inhibits a step in mammalian secretory pathways. We also demonstrate expression of CD39-L4 message in macrophages, suggesting that the protein is present in the circulation. Furthermore, we show that CD39-L4 is an E-type apyrase, is dependent on calcium and magnesium cations, and has high degree of specificity for NDPs over NTPs as enzymatic substrates. A potential physiological role in hemostasis and platelet aggregation is presented.