Homocysteine

This is an amino acid that is not part of the protein composition. It is homologous to the amino acid methionine that is part of proteins. The only difference is one (-CH₂) group. Homocysteine is formed during the metabolism of the amino acid methionine. Methionine is abundant in animal proteins. Homocysteine is an intermediate product of methionine metabolism and in properly nourished individuals, it does not accumulate excessively in the body. Homocysteine has a significant impact on the circulatory system. Elevated homocysteine concentration in blood plasma is considered a risk factor that promotes atherosclerosis and disorders and diseases of blood vessels, especially those of the heart, brain, and peripheral circulation. Excess homocysteine damages the walls of arteries. The increase in homocysteine in the blood plasma of healthy individuals depends on an unbalanced diet. Older individuals generally have higher homocysteine concentrations in their blood plasma than younger individuals. The normal concentration of homocysteine in the blood plasma of adults is 1.4–13.1 µmol/litre. During metabolism, the regulation of methionine remethylation (conversion of homocysteine back to methionine) depends on dietary factors such as multivitamins and minerals, but the most important are B-group vitamins – folates, vitamin B₁₂, and vitamin B₆, which are essential for homocysteine metabolism. It has been found that additional intake of folates, vitamins B₁₂, and B₆ normalizes the concentration of homocysteine in blood plasma, even if methionine is consumed in excess.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė