Is adenosine deaminase involved in adenosine transport?
The hypothesis that adenosine metabolizing enzymes may have a key role in the transport of adenosine is discussed. The enhancement of adenosine transport by inhibitors of adenosine deaminase (the enzyme which deaminates adenosine to inosine) and the ecto-localization of adenosine deaminase suggest a contribution of the enzyme in taking up nucleosides. Two possible mechanisms are suggested: 1) transport and deamination of adenosine as a coupled process, or 2) uptake of inosine after cleavage of adenosine by ecto-adenosine deaminase. In both cases, the so-called adenosine deaminase binding protein which is a membrane protein could be the real nucleoside transporter. This behaviour of adenosine deaminase as an ectoenzyme anchored to a membrane protein remembers the behaviour of periplasmic binding proteins of bacteria. Thus, adenosine deaminase as well as, for instance, adenosine kinase would be a kind of 'periplasmic proteins' of eukaryotic cells. The function of adenosine deaminase and adenosine kinase would then be to take adenosine and give it to the true transporters.
Centelles
J J
JJ
Department of Biochemistry and Physiology, School of Chemistry, Barcelona, Spain.
Franco
R
R
D000241:Adenosine / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D008954:Models, Biological
D002352:Carrier Proteins; D000243:Adenosine Deaminase; D000241:Adenosine