ho·mo·cys·te·ine 
(hō′mə-sĭstə-ēn′, -ĭn, -tē-)
(hō′mə-sĭstə-ēn′, -ĭn, -tē-)n.
An amino acid, C4H9NO2S, not found in proteins, that is used by the body in cellular metabolism. Elevated concentrations in the blood are associated with an increased risk of heart disease.
[homo-, homologous with (from HOMOLOGOUS) + CYSTEINE.]