New Insights into the Roles of Cysteine and Homocysteine in Pathological Processes IntechOpen Homocysteine: Diagnostic Significance and Clinical Insights Advanced Health Academy Dermedical Skin Sciences 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,