S-Adenosyl-L-homocysteine (SAH) is an amino acid derivative and an intermediate, by-product, or modulator of several metabolic pathways, including the activated methyl cycle and cysteine biosynthesis. It is also a product of S-adenosyl-methionine (SAM)-dependent methylation of biological molecules, including DNA, RNA, and histones and other proteins. SAH is a risk factor for many diseases, including cancer and neurodegenerative diseases.
