Purification and comparison of two forms of S-adenosyl-L-methionine synthetase from rat liver.
Only two S-adenosyl-L-methionine synthetase forms exist in rat liver: high-Mr S-adenosyl-L-methionine synthetase and low-Mr S-adenosyl-L-methionine synthetase, which have been purified to apparent homogeneity as judged by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. High-Mr S-adenosyl-L-methionine synthetase had an apparent molecular mass, determined by gel filtration, of 210 kDa and was a tetramer constituted by 48.5-kDa subunits, estimated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The apparent molecular mass of low-Mr S-adenosyl-L-methionine synthetase, as estimated by gel filtration, was 110 kDa and was constituted by two subunits of 47 kDa. An antiserum against low-Mr S-adenosyl-L-methionine synthetase cross-reacted with the two forms. Reverse-phase HPLC runs of tryptic digestions of high-Mr and low-Mr S-adenosyl-L-methionine synthetase showed that the peptide maps of the two forms were very similar, if not identical. High-Mr S-adenosyl-L-methionine synthetase activity was inhibited by S-adenosyl-L-methionine and pyrophosphate. Depending on the dose used, S-adenosyl-L-methionine activated or inhibited low-Mr S-adenosyl-L-methionine synthetase and pyrophosphate had no effect on this form. The two synthetases showed a different specific activity at the physiological concentration of methionine. This report shows that even though the two forms are constructed of the same polypeptide chains, they are regulated in a different manner by methionine and by the products of the reaction.
D000818:Animals; D002850:Chromatography, Gel; D005779:Immunodiffusion; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008716:Methionine Adenosyltransferase / Q000302:isolation & purification* / Q000378:metabolism; D010449:Peptide Mapping; D051381:Rats; D014166:Transferases / Q000302:isolation & purification*
D007527:Isoenzymes; D014166:Transferases; D008716:Methionine Adenosyltransferase