Glutathione (GSH) is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain. It is an antioxidant, preventing damage to important cellular components caused by reactive oxygen species such as free radicals and peroxides.
Thiol groups are reducing agents, existing at a concentration of approximately 5 mM in animal cells. Glutathione reduces disulfide bond formed within cytoplasmic proteins to cysteines by serving as an electron donor. In the process, glutathione is converted to its oxidized form glutathione disulfide (GSSG). Glutathione is found almost exclusively in its reduced form, since the enzyme that reverts it from its oxidized form, glutathione reductase, is constitutively active and inducible upon oxidative stress. In fact, the ratio of reduced glutathione to oxidized glutathione within cells is often used scientifically as a measure of cellular toxicity.
Glutathione is not an essential nutrient, since it can be synthesized from the amino acids L-cysteine, L-glutamic acid, and glycine. The sulfhydryl (thiol) group (SH) of cysteine serves as a proton donor and is responsible for the biological activity of glutathione. Provision of this amino acid is the rate-limiting factor in glutathione synthesis by the cells, since cysteine is relatively rare in foodstuffs. Furthermore, if released as the free amino acid, cysteine is toxic and spontaneously catabolized in the gastrointestinal tract and blood plasma.
Glutamine is the most abundant amino acid found in human muscle and is supplemented because supplement manufacturers claim the body's natural glutamine levels are depleted during anaerobic exercise. It is argued that bodybuilders should supplement with glutamine, as deficiency may lead to a weakened immune system and wasting of muscle tissue. It is sold as a micronized, instantly soluble powder. Some studies have shown there to be no significant effect of glutamine on bench press strength, knee-extension torque or lean muscle mass when compared to controls taking a placebo, though another study found that glutamine is beneficial in raising T-helper/suppressor cell ratio in long distance runners.
During intense exercise the body produces lactic acid for energy. The lactate is used up for energy and the hydrogen is left, dropping the pH in the muscle, causing a ‘burning’ fatigue. One of the amino acids that your body uses to counteract this acidosis caused by the lactic acid is the glutamine in your bloodstream. In order to replenish the loss of glutamine in the bloodstream, the body catabolises glutamine from the muscle. So supplementing with glutamine ensures there is always a constant supply for the muscles.