Relative Roles of Albumin and Ceruloplasmin in the Formation of Homocystine, Homocysteine-Cysteine-mixed Disulfide, and Cystine in Circulation

Shantanu Sengupta, Charles Wehbe, Alana K. Majors, Michael E Ketterer, Patricia M. DiBello, Donald W. Jacobsen

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108 Scopus citations


Disulfide forms of homocysteine account for >98% of total homocysteine in plasma from healthy individuals. We recently reported that homocysteine reacts with albumin-Cys34-S-S-cysteine to form homocysteine-cysteine mixed disulfide and albumin-Cys34 thiolate anion. The latter then reacts with homocystine or homocysteine-cysteine mixed disulfide to form albumin-bound homocysteine (Sengupta, S., Chen, H., Togawa, T., DiBello, P. M., Majors, A. K., Büdy, B., Ketterer, M. E., and Jacobsen, D. W. (2001) J. Biol. Chem. 276, 30111-30117). We now extend these studies to show that human albumin, but not ceruloplasmin, mediates the conversion of homocysteine to its low molecular weight disulfide forms (homocystine and homocysteine-cysteine mixed disulfide) by thiol/disulfide exchange reactions. Only a small fraction of homocystine is formed by an oxidative process in which copper bound to albumin, but not ceruloplasmin, mediates the reaction. When copper is removed from albumin by chelation, the overall conversion of homocysteine to its disulfide forms is reduced by only 20%. Ceruloplasmin was an ineffective catalyst of homocysteine oxidation, and immunoprecipitation of ceruloplasmin from human plasma did not inhibit the capacity of plasma to mediate the conversion of homocysteine to its disulfide forms. In contrast, ceruloplasmin was a highly efficient catalyst for the oxidation of cysteine and cysteinylglycine to cystine and bis(-S-cysteinylglycine), respectively. However, when thiols (cysteine and homocysteine) that are disulfide-bonded to albumin-Cys34 are removed by treatment with dithiothreitol to form albumin-Cys34-SH (mercaptalbumin), the conversion of homocysteine to its disulfide forms is completely blocked. In conclusion, albumin mediates the formation of disulfide forms of homocysteine by thiol/disulfide exchange, whereas ceruloplasmin converts cysteine to cystine by copper-dependent autooxidation.

Original languageEnglish (US)
Pages (from-to)46896-46904
Number of pages9
JournalJournal of Biological Chemistry
Issue number50
StatePublished - Dec 14 2001
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry

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