title: Adenosine metabolism in wild-type and enzyme-deficient variants of Chinese hamster ovary and Novikoff rat hepatoma cells.
abstract: Variants of Chinese hamster ovary and Novikoff rat hepatoma cells resistant to tubercidin and 2,5-diaminopurine, or to both drugs, were isolated, and their ability to convert adenosine and various adenosine analogs to nucleotides was compared to that of wild-type cells, both in intact cells and cell-free extracts. Adenosine deamination, and thus its conversion to nucleotides via inosine-hypoxanthine-inosine monophosphate, was inhibited by pretreatment of the cells or cell extracts with 2-deoxycoformycin. Cell-free extracts of the tubercidin-resistant variants, as well as of two adenosine-resistant mutants of Chinese hamster ovary cells, phosphorylated adenosine, tubercidin, pyrazofurin, or tricyclic nucleoside in the presence of ATP at less than 1% of the rate of extracts of wild-type cells. However, addition of phosphoribosyl pyrophosphate stimulated the conversion of adenosine to nucleotides 40-fold. Similarly, intact adenosine kinase-deficient cells failed to phosphorylate the adenosine analogs, but still converted adenosine to nucleotides at 5-10% the rate observed with wild-type cells. Phosphorylation of adenosine and tubercidin in wild-type cells was inhibited by substrate at concentration above 5-10 microM. In contrast, the rate of conversion of adenosine to nucleotides by adenosine kinase-deficient cells increased linearly up to a concentration of 400 microM adenosine, with the consequence that, at this concentration, these cells took up adenosine almost as rapidly as wild-type cells. Adenosine uptake by these kinase-deficient cells was inhibited by adenine and 5'-deoxyadenosine, and was largely abolished in mutants devoid also of adenine phosphoribosyltransferase. We conclude that adenosine is converted to nucleotides in adenosine kinase-deficient cells via adenine. Indirect evidence implicates 5'-methylthioadenosine phosphorylase as the enzyme responsible for the degradation of adenosine to adenine.
mesh_terms: D015075:2-Aminopurine / Q000031:analogs & derivatives / Q000494:pharmacology; D000227:Adenine Nucleotides / Q000378:metabolism*; D000241:Adenosine / Q000378:metabolism*; D000248:Adenosine Kinase / Q000172:deficiency*; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002474:Cell-Free System; D003070:Coformycin / Q000031:analogs & derivatives / Q000494:pharmacology; D006224:Cricetinae; D005260:Female; D007700:Kinetics; D008114:Liver Neoplasms, Experimental; D010053:Ovary; D015649:Pentostatin; D010766:Phosphorylation; D010770:Phosphotransferases / Q000172:deficiency*; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism; D051381:Rats; D014372:Tubercidin / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D003070:Coformycin; D015649:Pentostatin; D015075:2-Aminopurine; C007300:2,6-diaminopurine; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D010770:Phosphotransferases; D000248:Adenosine Kinase; D000241:Adenosine; D014372:Tubercidin