Cysteine

Overview

Cysteine is a non-essential amino acid formed from the essential amino acids methionine and phenylalanine that is synthesized in the Liver. Cysteine and Cystine readily convert to one another and have almost identical functions within the body. Cystine is the less desirable form than Cysteine.

Cysteine may Enhance the Function of these Substances

Amino Acids 

 Cystine is formed by linking two Cysteine molecules by their Sulfur atoms.  ^[1]

 Taurine can be manufactured within the body from Cysteine.  ^[2] 

Carbohydrates

 Cysteine is metabolized to form endogenous Glucose within the Liver.  ^[3] 

Coenzymes

 Cysteine is utilized in the synthesis of Coenzyme A. 

Enzymes

 Cysteine especially the N-Acetyl Cysteine (NAC) form of Cysteine protects Alpha-1 Antitrypsin by preventing the oxidation of methionine residues within this protein.  ^[4]

 Cysteine is an essential constituent of the Glutathione Peroxidase enzyme. 

Hormones 

 Cysteine is an essential constituent of the Glucose Tolerance Factor (GTF) molecule.

Minerals 

 Cysteine is the preferred Amino Acid for chelation with Iron. 

 Sulfur comprises 26% of the Cysteine molecule which is why Cysteine is a good supplemental source of sulfur. 

Nucleic Compounds

 Cysteine may participate in repairing some forms of Deoxyribonucleic Acid (DNA) within the body.  ^[5]  

Peptides 

 Cysteine is an essential constituent of Glutathione:  ^[6]

 The N-Acetyl-Cysteine (NAC) form of Cysteine increases Glutathione levels more effectively than exogenous Cysteine.

 Of the several precursors for Glutathione, Cysteine is believed to be the most important as the other precursors (Glycine and Glutamic Acid) are generally not deficient.  This means that Cysteine is generally the rate-limiting factor in Glutathione production.

 Cysteine appears to be the rate-limiting Amino Acid (of the three Amino Acids) precursor of Glutathione production. 

Vitamins  

 Folic Acid is a cofactor for the conversion of Methionine to Cysteine.

 Vitamin B6 may enhance the function of Cysteine.  ^[7]