title: S-adenosylhomocysteine inhibition of three purified tRNA methyltransferases from rat liver.
abstract: Three tRNA methyltransferases from rat liver have been fractionated and purified greater than 100-fold. These enzymes have been examined for their sensitivity to inhibition by S-adenosylhomocysteine (SAH). The methyltransferase which forms m2-guanine in the region between the dihydrouridine loop and the acceptor stem of tRNA (m2-guanine methyltransferase I) is least sensitive to SAH inhibition, with a Ki of 8 muM. The enzyme responsible for forming m2-guanine between the dihydrouridine and anticodon loops (m2-guanine methyltransferase II) has a Ki of 0.3 muM, while m1-adenine methyltransferase shows intermediate sensitivity to SAH (Ki = 2.4 muM). All three methyltransferases have similar Km's for the S-adenosylmethionine substrate (1.5-2.0 muM). These results are consistent with the hypothesis that activity of individual tRNA methyltransferases may be controlled by enzyme systems which alter cellular SAH levels.
mesh_terms: D000225:Adenine; D000818:Animals; D006147:Guanine; D006710:Homocysteine / Q000031:analogs & derivatives*; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051381:Rats; D012435:S-Adenosylhomocysteine / Q000494:pharmacology; D013329:Structure-Activity Relationship; D012359:tRNA Methyltransferases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification
chemical_list: D007527:Isoenzymes; D006710:Homocysteine; D006147:Guanine; D012435:S-Adenosylhomocysteine; D012359:tRNA Methyltransferases; D000225:Adenine