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Effect of Ligand Structure on the Pathways for Iron Release from Serum Transferrin

Brook, C.E; Harris, W.R; Spilling, C.D; Peng, W; Harburn, J.J; Srisung, S

Authors

C.E Brook

W.R Harris

C.D Spilling

W Peng

J.J Harburn

S Srisung



Abstract

Rate constants for the removal of iron from N-terminal monoferric transferrin have been measured for a series of phosphate and phosphonocarboxylic acids in pH 7.4 0.1 M hepes buffer at 25 °C. The bidentate ligands pyrophosphate and phosphonoacetic acid (PAA) show a combination of saturation and first-order kinetics with respect to the ligand concentration. Similar results are observed following a single substitution at the 2-position of PAA to give 2-benzyl-PAA and phosphonosuccinic acid. In contrast, disubstitution at the 2-position to form 2,2-dibenzyl-PAA leads to a marked reduction in iron removal via the first-order pathway. Rate constants were also measured for tripolyphosphate and phosphonodiacetic acid, which are elongated versions of PPi and PAA. In both cases, this elongation completely eliminates the first-order component for iron release while having relatively little impact on the saturation pathway. The sensitivity of the first-order component to the structure of the ligand strongly indicates that this pathway involves the binding of the ligand to a specific site on the protein and cannot be attributed to changes in the overall ionic strength of the solution as the ligand concentration increases. It is proposed that this structural sensitivity reflects steric restrictions on the ability of the incoming ligand to substitute for the synergistic carbonate anion to form a relatively unstable Fe−ligand−Tf ternary intermediate, which then dissociates to FeL and apoTf.

Citation

Brook, C., Harris, W., Spilling, C., Peng, W., Harburn, J., & Srisung, S. (2005). Effect of Ligand Structure on the Pathways for Iron Release from Serum Transferrin. Inorganic Chemistry, 44(14), 5183-5191. https://doi.org/10.1021/ic050411m

Journal Article Type Article
Publication Date Jun 1, 2005
Deposit Date Oct 29, 2012
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 44
Issue 14
Pages 5183-5191
DOI https://doi.org/10.1021/ic050411m