Characterization of transferrin metal-binding sites by diffusion-enhanced energy transfer

Simon M. Yeh, Claude F. Meares

Research output: Contribution to journalArticle

38 Scopus citations

Abstract

The distance from the protein surface to ferric or manganic ions in the two specific metal-binding sites of human serum transferrin has been estimated by measuring energy transfer from freely diffusing terbium chelates in aqueous solution to transferrin-bound metal ions. In addition, both monoferric forms of the protein were studied, as well as the diferric complex formed by using oxalate instead of (bi)carbonate as the auxiliary anion in binding of iron(III) to transferrin. Second-order rate constants for energy transfer between electrically neutral terbium(III)-N-(2-hydroxy-ethyl)ethylenediaminetriacetate and the FeA, FeB, and Fe2 forms of transferrin were 0.9 × 105 M-1 s-1, 1.4 × 105 M-1 s-1, and 2.6 × 105 M-1 s-1, respectively (based on iron concentration). For the Fe2 species, substitution of oxalate for (bi)carbonate has the effect of decreasing the accessibility of both electrically neutral and negatively charged terbium chelates to the protein-bound iron chromophores. Theoretical considerations of the effect of acceptor location in the protein on energy transfer suggest that the iron chromophores are not on the surface of the protein but are <1.7 nm below the surface. The use of diterbium transferrin as energy donor to a small cobalt chelate in solution or to diferric transferrin corroborates these results.

Original languageEnglish (US)
Pages (from-to)5057-5062
Number of pages6
JournalBiochemistry
Volume19
Issue number22
StatePublished - 1980

ASJC Scopus subject areas

  • Biochemistry

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