Inactivation and reactivation of intracellular S-adenosylhomocysteinase in the presence of nucleoside analogues in rat hepatocytes.
Several nucleoside analogues, some of which are potent inactivators of isolated S-adenosylhomocysteinase (AdoHcyase), were tested with respect to their effect on intracellular AdoHcyase and S-adenosylhomocysteine (AdoHcy) catabolism in intact rat hepatocytes. Among the analogues tested, 9-beta-D-arabinofuranosyladenine and 9-beta-D-arabinofuranosyl-3-deazaadenine were the most potent inactivators of intracellular AdoHcyase. Compounds like 2-chloroadenosine and carbocyclic adenosine are extremely efficient inactivators of the isolated enzyme, but these nucleosides exerted only a limited effect on the enzyme in intact hepatocytes. Only a moderate effect was observed with 2-chloro-3-deazaadenosine and 2'-deoxyadenosine, and a high concentration of 5'-deoxy-5'-methylthioadenosine was required to inactivate the enzyme. There was a correlation between inactivation and accumulation of AdoHcy. Carbocyclic-3-deazaadenosine caused no inactivation of AdoHcyase in liver cells but caused a massive accumulation of AdoHcy, suggesting that this analogue functions as a reversible inhibitor of the enzyme. Residual enzyme activity was observed with all the nucleoside analogues tested. The intracellular enzyme inactivated in the presence of 2'-deoxyadenosine and 9-beta-D-arabinofuranosyladenine was readily recovered when the cells were transferred to fresh medium containing adenosine deaminase, but reactivation of the enzyme activity after treatment of the cells with 2-chloroadenosine and 5'-deoxy-5'-methylthioadenosine was also observed. The inactivation of intracellular enzyme induced by 2-chloro-3-deazaadenosine, 9-beta-D-arabinofuranosyl-3-deazaadenine, and carbocyclic adenosine was essentially irreversible under the conditions of the experiments. Factors determining the effect of nucleoside analogues on intracellular AdoHcyase are discussed.
D043383:Adenosylhomocysteinase; D000818:Animals; D006867:Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009705:Nucleosides / Q000494:pharmacology*; D051381:Rats; D012435:S-Adenosylhomocysteine / Q000032:analysis; D012436:S-Adenosylmethionine / Q000032:analysis; D013329:Structure-Activity Relationship; D014740:Vidarabine / Q000032:analysis
D009705:Nucleosides; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D006867:Hydrolases; D043383:Adenosylhomocysteinase; D014740:Vidarabine