The proposed 5'-nucleotidase inhibitor in human leukemic cells is an artefact.
It is now well established that human lymphoblastoid cell lines showing immaturity characters display ecto-5'-nucleotidase activities lower than normal levels. A recent paper (Sun, A.S., Holland, J.F. and Ohnuma, T. (1983) Biochim. Biophys. Acta 762, 577-584) mentioned that this phenomenon resulted from the presence of a 5'-nucleotidase inhibitor in these cell lines. We demonstrate here that the use of 5'-[3H]AMP as a substrate, and inadequate analysis of the products formed, led them to a misinterpretation. [3H]Adenosine derived from 5'-[3H]AMP hydrolysis was further transformed into [3H]inosine by the adenosine deaminase activity of the leukemic cell lines tested; [3H]inosine was precipitated with the excess substrate and was not taken into account in the ecto-5'-nucleotidase determination, which led the authors to confuse this adenosine deaminase activity with a 5'-nucleotidase inhibitor. We did not observe 5'-nucleotidase inhibition by leukemic cell cytosol when convenient assay methods were used and showed that the presence of such an inhibitor remains to be established.
D015720:5'-Nucleotidase; D000241:Adenosine / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D006801:Humans; D007288:Inosine / Q000378:metabolism; D007938:Leukemia / Q000201:enzymology*; D009708:Nucleotidases / Q000037:antagonists & inhibitors*
D000249:Adenosine Monophosphate; D007288:Inosine; D009708:Nucleotidases; D015720:5'-Nucleotidase; D000243:Adenosine Deaminase; D000241:Adenosine