Homocysteine is a protein amino acid in humans: Implications for homocysteine-linked disease

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Homocysteine is thought to be a non-protein amino acid. However, in vitro studies suggest that homocysteine is likely to be incorporated by indirect mechanisms into proteins in living organisms. Here I show that homocysteine is a protein amino acid in humans. Homocysteine bound by amide or peptide linkages (HcyN-protein) is present in human hemoglobin, serum albumin, and γ-globulins. 1 molecule of homocysteine per 1000 or 1670 molecules of methionine was present in hemoglobin or albumin, respectively. Other proteins, such as low density lipoprotein, high density lipoprotein, transferrin, antitrypsin, and fibrinogen, contained lower amounts of Hcy-N-protein. In human plasma, levels of Hcy-N-protein represented from 0.3 to 23% of total homocysteine. Thus, Hcy-N-protein is a significant component of homocysteine metabolism in humans, possibly contributing to adverse effects of homocysteine on human cells.

Original languageEnglish (US)
Pages (from-to)30425-30428
Number of pages4
JournalJournal of Biological Chemistry
Issue number34
StatePublished - Aug 23 2002

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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