L Methionine Endogenous Metabolite MedChemExpress Amazon.com: Pure Encapsulations L Methionine Glutathione and Amino Acid Supplement for Joints, Liver and Pancreas Support, Antioxidants, and Nervous System* 60 Capsules : Health & Household Homocysteine and methionine are key amino acids with a vital connection to glutathione one of your body's most important substances! Methionine is abundant in many foods, so protein isn't the culprit, Homocysteine: Diagnostic Significance and Clinical Insights Advanced Health Academy Sulfur metabolism under stress: Oxidized glutathione inhibits methionine biosynthesis by destabilizing the enzyme cystathionine < em> synthase