MAT1A (Methionine Adenosyltransferase I, Alpha) is an enzyme that produces S-adenosylmethionine (SAMe), the body’s main methyl donor for essential metabolic processes. It plays a key role in methionine metabolism, affecting gene regulation, cell growth, and detoxification. Reduced MAT1A activity is associated with liver conditions such as cirrhosis and hepatocellular carcinoma.