Figure 6
Pathways for sulfate reduction and synthesis of cysteine and methionine. The essential amino acids lysine, threonine, isoleucine and methionine are synthesized from the same precursor aspartic acid. Methionine is a sulfur-containing amino acid, in which the sulfur moiety is transferred from cysteine by CGS. The sulfide in cysteine is reduced from sulfate absorbed from the soil by three steps as shown in the diagram.