<prompt> Most important amino acid which acts as methyl group donor-CysteineMethionineTyrosineTryptophan  <response>: Ans. is b i.e., Methionineo Methionine is activated into S-adenosylmethionine, which then transfers its methyl group to an acceptor. Thus methionine acts as methyl donor in transmethylation reactions.o Some of the important transmethylation reactions are-i Norepinephrine - Epinephrineii Phosphatidylethanolamine - Phosphatidylcholineiii Gunaidoacetate - Creatineiv Ethanolamine - Cholinev Acetyl serotonin - Serotoninvi Nucleotides - methylated nucleotides 