title: Distinct roles for recombinant cytosolic 5'-nucleotidase-I and -II in AMP and IMP catabolism in COS-7 and H9c2 rat myoblast cell lines.
abstract: Catabolism of AMP during ATP breakdown produces adenosine, which restores energy balance. Catabolism of IMP may be a key step regulating purine nucleotide pools. Two, cloned cytosolic 5'-nucleotidases (cN-I and cN-II) have been implicated in AMP and IMP breakdown. To evaluate their roles directly, we expressed recombinant pigeon cN-I or human cN-II at similar activities in COS-7 or H9c2 cells. During rapid (more than 90% in 10 min) or slower (30-40% in 10 min) ATP catabolism, cN-I-transfected COS-7 and H9c2 cells produced significantly more adenosine than cN-II-transfected cells, which were similar to control-transfected cells. Inosine and hypoxanthine concentrations increased only during slower ATP catabolism. In COS-7 cells, 5'-nucleotidase activity was not rate-limiting for inosine and hypoxanthine production, which was therefore unaffected by cN-II- and actually reduced by cN-I- overexpression. In H9c2 cells, in which 5'-nucleotidase activity was rate-limiting, only cN-II overexpression accelerated inosine and hypoxanthine formation. Guanosine formation from GMP was also increased by cN-II. Our results imply distinct roles for cN-I and cN-II. Under the conditions tested in these cells, only cN-I plays a significant role in AMP breakdown to adenosine, whereas only cN-II breaks down IMP to inosine and GMP to guanosine.
authors.affiliation: University of Bristol, Bristol Heart Institute, Bristol BS2 8HW, United Kingdom. G.Newby@bris.ac.uk
authors.forename: G B
authors.initials: GB
authors.lastname: Sala-Newby
authors.forename: N V
authors.initials: NV
authors.lastname: Freeman
authors.forename: A C
authors.initials: AC
authors.lastname: Skladanowski
authors.forename: A C
authors.initials: AC
authors.lastname: Newby
mesh_terms: D015720:5'-Nucleotidase / Q000235:genetics / Q000502:physiology*; D000241:Adenosine / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D010856:Columbidae; D003600:Cytosol / Q000201:enzymology; D004734:Energy Metabolism; D006321:Heart / Q000196:embryology; D006801:Humans; D019271:Hypoxanthine / Q000378:metabolism; D007291:Inosine Monophosphate / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology*; D007700:Kinetics; D009132:Muscles / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D007291:Inosine Monophosphate; D019271:Hypoxanthine; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase; D000241:Adenosine