This review article discusses the roles of sulfur-containing amino acids—methionine, cysteine, homocysteine, and taurine—in human biochemistry. Methionine, an essential amino acid, is involved in methylation reactions and protein synthesis, while cysteine plays a crucial role in protein structure and is the precursor for glutathione and taurine. The metabolism of homocysteine,
This observational study investigated the pharmacokinetics of glutathione (GSH) and its metabolites—cysteine (Cys), cystine (Cys2), and methionine (Met)—in healthy individuals to determine optimal dosing for reducing reactive oxygen species (ROS), especially in cases like paraquat poisoning. It found that Cys and Met effectively suppressed ROS production in a dose-dependent manner,
This in vitro study compared the redox activity of four thiol compounds—glutathione (GSH), N-acetylcysteine (NAC), cysteine (Cys), and homocysteine (HCS)—to evaluate their potential to reduce molecular oxygen and influence oxidative or reductive stress. The researchers found that GSH and Cys can reduce O₂ to generate reactive oxygen species (ROS), particularly
This study examined the effects of supplementing cysteine and glycine—precursors to glutathione (GSH)—in older HIV-infected men with GSH deficiency. Over 14 days, participants received oral cysteine and glycine supplementation, which restored GSH synthesis. As a result, the study reported significant improvements in both fasting and insulin-stimulated mitochondrial fuel oxidation, insulin
This systematic review evaluates how supplementation with glutathione (GSH) precursor amino acids—particularly cysteine, glycine, and glutamate—as well as non-precursor amino acids, micronutrients (such as vitamins C and E), and overall dietary patterns influence glutathione homeostasis and antioxidant defense. Because orally consumed GSH is inefficiently absorbed due to intestinal degradation, enhancing
