Cysteine
Cysteine is an important structural and functional component of proteins and enzymes. It also has the ability to break down proteins found in mucous that settles in the lungs. As a result, this amino acid may be useful in the treatment of bronchitis and other respiratory problems. But most importantly- the antioxidant activity of Glutathione (GSH) is attributed specifically to the presence and availability of cysteine. As a result, low levels of this all-important amino acid may reduce one's ability to prevent free radical damage and may result in impaired function of the immune system. If cysteine is good for boosting immune system, the logical question is why not to eat it as a supplement? It has been shown that taking cysteine (L-cysteine) as a supplement may in fact raise Glutathione to some degree. But cysteine taken this way (as a supplement) is potentially toxic. Cysteine toxicity leads to a number of disorders in the body, from heart disease to renal (kidney) disease. Due to the potential for cysteine toxicity, excessive homocysteine and hypercysteinemia, it is not recommended to take L-cysteine supplements without strict supervision from your physician. To help understand cysteine, Dr. Allan Somersall and Dr. Gustavo Bounous in the book "Breakthrough in Cell-Defense" state the following: "...three bioactive proteins contained in the milk serum and which are all sensitive to heat in a liquid phase...lactoferrin, serum albumin and alpha lactalbumin... contain exceptional amounts of cysteine, the critical rate limiting molecular precursor of glutathione. More importantly, it is the form of cysteine which is present that is so critical. The cysteine does occur in pairs in different parts of the protein chains. Cystine is the name of this so-called dipeptide unit. Note the different spelling of cystine (the dipeptide) and cysteine (the amino acid). In fact, cysteine occurs in two different dipeptide units, i.e. cystine (cys-cys) and glutamyl cysteine (glu-cys). These dipeptides are held together by the disulfide (S-S) bridges which can be kept undenatured under stringent conditions and even remain undigested for absorption into cells. Therein lies the Breakthrough...it has been demonstrated that the Glu-Cys precursors of GSH can easily enter the cell to be synthesized into GSH." What all this is saying is simply that all forms of cysteine are not equal, and that for cysteine to be available to enter the cell for Glutathione production it must be consumed in a proper form (as a dipeptide, bonded, undenatured). Mother's milk contains lactoferrin, serum albumin and alpha lactalbumin, as well as other immunoglobulins. This is one of the reasons why mother's milk is such a strong immune system builder for the baby immune system. Production of cysteine in the body depends on the availability of several other nutrients: methionine, vitamins B1, B2, B6, B12, folate and selenium. Dietary deficiency of these nutrients may decrease the production of cysteine. Daily recommendation for dietary cysteine intake is 700 mg for men and 575 mg for women (established by the National Academy of Sciences and published as Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients), National Academies Press, 2005). However, these numbers do not reflect the individual needs for cysteine that depend on one's current health condition because at the time of a disease and depending on its severity more Glutathione (and thus, cysteine) is used by the body to eliminate the threat. Compared to other amino acids cysteine content in food is rather low.
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