Methionine is an essential amino acid, which animals cannot synthesize. In bacteria and plants, methionine is synthesized from aspartate [MD:M00017]. S-Adenosylmethionine (SAM), synthesized from methionine and ATP, is a methyl group donor in many important transfer reactions including DNA methylation for regulation of gene expression. SAM may also be used to regenerate methionine in the methionine salvage pathway Pathway adapted from [KEGG](http://www.kegg.jp/kegg-bin/show_pathway?map00270). Proteins on this pathway have targeted assays available via the [CPTAC Assay Portal](https://assays.cancer.gov/available_assays?wp_id=WP3580). aec ec0 map00270 KEGG Pathway Cysteine and methionine metabolism https://www.kegg.jp/dbget-bin/www_bget?pathway+map00270 8393662 PubMed Characterization of a full-length cDNA encoding human liver S-adenosylmethionine synthetase: tissue-specific gene expression and mRNA levels in hepatopathies. Biochem J 1993 Alvarez L Corrales F Martin-Duce A Mato JM classic metabolic pathway PW:0000002 Pathway Ontology methionine biosynthetic pathway PW:0001301 Pathway Ontology