Partial purification and properties of the isozymes of S-adenosylmethionine synthetase from sheep liver.
Three forms of AdoMet synthetase were separated from sheep liver. The apparent molecular weights of the native isozymes were 122,000, 62,400 and 70,800 for the alpha-, beta 1- and beta 2-form, respectively and beta 1 was the predominant form. The alpha-form exhibited negative cooperativity with [S] 0.5 values of 31 microM for methionine and 62 microM for ATP; while the two beta-forms exhibited positive cooperativity with [S]0.5 values for methionine of 82 microM and 70 microM and those for ATP of 572 microM and 505 microM for the beta 1- and beta 2-form, respectively. Dimethylsulfoxide markedly stimulated the activities of the two beta-forms at low methionine concentrations. However, at high methionine levels, it inhibited the activity of the beta 2-form but not that of the beta 1-form. The effect of dimethylsulfoxide on the alpha-form was not significant. AdoMet was inhibitory at high concentrations. However, it had a slight stimulatory effect on the two beta-forms at low concentrations when methionine level was also low. These results suggest that AdoMet synthetase is a regulatory enzyme and the reaction rate in vivo can be directly influenced by substrate and product concentrations.
Department of Animal Sciences, Waite Agricultural Research Institute, University of Adelaide, South Australia.
G P
GP
Xue
A M
AM
Snoswell
R C
RC
Fishlock
D000818:Animals; D002845:Chromatography / Q000379:methods; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008715:Methionine / Q000494:pharmacology; D008716:Methionine Adenosyltransferase / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D008970:Molecular Weight; D012436:S-Adenosylmethionine / Q000494:pharmacology; D012756:Sheep / Q000378:metabolism*; D014166:Transferases / Q000302:isolation & purification*
D007527:Isoenzymes; D012436:S-Adenosylmethionine; D008715:Methionine; D014166:Transferases; D008716:Methionine Adenosyltransferase; D004121:Dimethyl Sulfoxide