Extracellular purines are important signalling molecules in the vasculature that are regulated by a network of cell surface ectoenzymes. By using human endothelial cells and normal and leukaemic lymphocytes as enzyme sources, we identified the following purine-converting ectoenzymes: (1) ecto-nucleotidases, NTP diphosphohydrolase/CD39 (EC 3.6.1.5) and ecto-5′-nucleotidase/CD73 (EC 3.1.3.5); (2) ecto-nucleotide kinases, adenylate kinase (EC 2.7.4.3) and nucleoside diphosphate kinase (EC 2.7.4.6); (3) ecto-adenosine deaminase (EC 3.5.4.4). Evidence for this was obtained by using enzyme assays with 3H-labelled nucleotides and adenosine as substrates, direct evaluation of γ-phosphate transfer from [γ-32P]ATP to AMP/NDP, and bioluminescent measurement of extracellular ATP synthesis. In addition, incorporation of radioactivity into an approx. 20kDa surface protein was observed following incubation of Namalwa B cells with [γ-32P]ATP. Thus two opposite, ATP-generating and ATP-consuming, pathways coexist on the cell surface, where basal ATP release, re-synthesis of high-energy phosphoryls, and selective ecto-protein phosphorylation are counteracted by stepwise nucleotide breakdown with subsequent adenosine inactivation. The comparative measurements of enzymic activities indicated the predominance of the nucleotide-inactivating pathway via ecto-nucleotidase reactions on the endothelial cells. The lymphocytes are characterized by counteracting ATP-regenerating/adenosine-eliminating phenotypes, thus allowing them to avoid the lymphotoxic effects of adenosine and maintain surrounding ATP at a steady-state level. These results are in agreement with divergent effects of ATP and adenosine on endothelial function and haemostasis, and provide a novel regulatory mechanism of local agonist availability for nucleotide- or nucleoside-selective receptors within the vasculature.
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October 2002
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Research Article|
October 01 2002
The evidence for two opposite, ATP-generating and ATP-consuming, extracellular pathways on endothelial and lymphoid cells Available to Purchase
Gennady G. YEGUTKIN;
Gennady G. YEGUTKIN
1
∗MediCity Research Laboratory, Turku University and National Public Health Institute, Tykistökatu 6A, FIN-20520 Turku, Finland,
1To whom correspondence should be addressed (e-mail [email protected]).
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Tiina HENTTINEN;
Tiina HENTTINEN
∗MediCity Research Laboratory, Turku University and National Public Health Institute, Tykistökatu 6A, FIN-20520 Turku, Finland,
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Sergei S. SAMBURSKI;
Sergei S. SAMBURSKI
∗MediCity Research Laboratory, Turku University and National Public Health Institute, Tykistökatu 6A, FIN-20520 Turku, Finland,
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Jozef SPYCHALA;
Jozef SPYCHALA
†Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599-7295, U.S.A.
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Sirpa JALKANEN
Sirpa JALKANEN
∗MediCity Research Laboratory, Turku University and National Public Health Institute, Tykistökatu 6A, FIN-20520 Turku, Finland,
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Publisher: Portland Press Ltd
Received:
March 19 2002
Revision Received:
May 28 2002
Accepted:
July 05 2002
Accepted Manuscript online:
July 05 2002
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2002
2002
Biochem J (2002) 367 (1): 121–128.
Article history
Received:
March 19 2002
Revision Received:
May 28 2002
Accepted:
July 05 2002
Accepted Manuscript online:
July 05 2002
Citation
Gennady G. YEGUTKIN, Tiina HENTTINEN, Sergei S. SAMBURSKI, Jozef SPYCHALA, Sirpa JALKANEN; The evidence for two opposite, ATP-generating and ATP-consuming, extracellular pathways on endothelial and lymphoid cells. Biochem J 1 October 2002; 367 (1): 121–128. doi: https://doi.org/10.1042/bj20020439
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