2.1.1.11 in complex with S-adenosylmethionine and S-adenosylhomocysteine at resolutions of 1.6 and 1.7 A, respectively. Conformational changes of the two arm regions may modulate binding and release of substrates/products to and from the active site. Residues Tyr28 and His 139 play essential roles for methyl transfer reaction but are not indispensable for cofactor/substrate binding 734272