Cysteine
A non-essential amino acid; one of the few amino acids that contains
sulfur which allows cysteine to bond in a special way and maintain
the structure of proteins in the body; as a component of glutathione,
cysteine provides glutathione with its biological potency and is a
powerful antioxidant (but can be oxidized with itself to form cysteine);
detoxification agent; component of some prostaglandins; an amino acid
transporter across membranes; the formation of cysteine from homocysteine
(another sulfur-containing amino acid) is one pathway to reduce an
elevated homocysteine status (elevated homocysteine is toxic to arteries,
thrombogenic, may promote oxidation of blood lipids, and moderate
hyperhomocysteinemia is an important independent risk factor for premature
vascular disease); produces the amino acid taurine which is used in
the formation of bile and nerve function; occasionally converted into
glucose and used as a source of energy; strengthens the protective
lining of the stomach and intestines which may help prevent damage
caused by aspirin and similar drugs; and plays an important role in
the communication between immune system cells.
A
cysteine deficiency could be a contributing cause of a decreased
ability to metabolize drugs and/or toxic compounds, depressed immune
functions, homocysteinemia, impaired antioxidant defenses and some
psychoses.
A deficiency
of any one or a combination of antioxidants could be a contributing
cause of arthritis, cancer, cardiovascular disease, diabetes, infections,
premature aging, renal disease, and a compromised immune system.
Antioxidants have also shown to be of benefit to individuals with
AIDS; several studies indicate that antioxidants help to stimulate
T-helper cells (primary cells destroyed by this disease), thus protecting
the immune system.
Clinical
trials using nutritional supplementation have shown therapeutic
benefits for alcoholism, allergies, asthma, bronchitis, cancer,
chronic obstructive pulmonary disease, cystic fibrosis, diabetes,
diabetic nephropathy, hair loss, heavy metal toxicity, HIV infection,
iron deficiency, reduction of cytotoxic treatment side effects,
seizure disorders and skin disorders.
Dietary
sources richest in N-acetyl-l-cysteine* (per serving) include eggs,
meats and meat products, milk, nutritional supplements, wheat germ,
whey protein and yogurt.
* Some
cysteine is oxidized to cystine and other compounds during cooking
and storage, and is thus less available to the body. In addition,
cysteine is the limiting amino acid in the intracellular function
of glutathione and is not recommended for supplementation, as it
is poorly tolerated by many individuals. Further, cysteine may be
rapidly oxidized to cystine - a less useable form for the synthesis
of glutathione. Therefore, supplementation with N-acetyl-l-cysteine
is the recommended form of supplementation to correct a cysteine
deficiency.
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