Homocysteine is an intermediary metabolite of the amino acid methionine. Homocystine is a double molecule of homocysteine. These amino acids are problems that cause a buildup of homocystine. The disease called homocystinuria can cause problems of the vascular system (advanced atherosclerosis), eyes, central nervous system, and also can create kidney stones. Excessive levels of these amino acids may also contribute to mental retardation or psychosis and have been implicated in speeding up the atherosclerotic process. Nutrients like B6 (important in many amino acid conversions), B12, folic acid, and cystine may reduce some of the problems of homocysteine genetic deficits.
Hydroxylysine is closely related to lysine and is important in the formation of collagen. It is also found in gelatin and in the digestive enzymes trypsin and chymotrypsin.
Hydroxyproline is an important component of collagen, which makes up the white, fibrous connective tissue and is part of the skin, bones, and cartilage. Hydroxyproline is converted from proline by hydroxylation only after proline gets into the amino acid chains that form body proteins.