Amino Acid Biosynthesis: Overview and Insights The Medical Biochemistry Page Glycine and N acetylcysteine (NAC) are amino acidbased nutrients that serve as precursors for glutathione, one of the body's most important intracellular antioxidants. Glutathione plays a central role in reducing oxidative stress, supporting Amino Acid Metabolism for Human Physiology Springer Nature Link Catabolism of extracellular glutathione supplies cysteine to support tumours Nature