Purification and Characterization of S-adenosylmethionine Synthetase from Wheat Embryos: Subunit Structure and Molecular Properties

S-adenosylmethionine synthetase from wheat embryos was purified to electrophoretic homogeneity. The mol wt of the enzyme was 174,000 as determined by molecular sieve chromatography on Sephacryl S-200. A single subunit of purified Ado Met synthetase was observed on SDS-PAGE with a mol wt of 84,000 suggesting that the enzyme is a homodimer. The apparent Km of purified enzyme with ATP and methionine is 80 jiM and 100 μM, respectively. The pH optimum of the enzyme is 7.75. The enzyme requires MgCl₂, KCI and reduced glutathione for optimum activity. The ³H-labelled putative S-adenosylmethionine reaction product was converted into ³H-Iabelled 5′-methyl-thioadenosine by heat treatment (100°C, 10 min, pH 7.0). This proved the authenticity of the reaction product of the AdoMet synthetase in wheat embryos.