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, What Are Amino Acids? Amino Acid Injections Explained Catabolism of extracellular glutathione supplies cysteine to support tumours Nature Newly revealed amino acid function could be used to boost antioxidant levels