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Negative cooperativity of chicken ovotransferrin on Al(III)-binding
K Ichimura1, H Kihara, T Yamamura
1Department of Chemistry, Faculty of Science, University of Tokyo.
Journal of Biochemistry
|July 1, 1989
Summary
Chicken ovotransferrin exhibits distinct metal-binding preferences. While cobalt(II) and aluminum(III) favor the N-site, terbium(III) prefers the C-site, with aluminum showing negative cooperativity.
Area of Science:
- Biochemistry
- Protein Chemistry
- Biophysical Chemistry
Background:
- Chicken ovotransferrin is an iron-binding protein with two distinct metal-binding sites: the amino (N) terminal and carboxy (C) terminal sites.
- It demonstrates the capacity to bind various metal ions, including Fe(III), Cu(II), Al(III), and Co(II).
Purpose of the Study:
- To investigate the selectivity and cooperativity of the N and C terminal sites of chicken ovotransferrin for Al(III), Co(II), and Tb(III) binding.
- To compare the binding cooperativity of these metal ions with previously observed Fe(III) and Cu(II) binding.
Main Methods:
- Investigated metal ion binding selectivity and cooperativity at the N and C terminal sites of chicken ovotransferrin.
- Quantified binding constants and cooperativity using a model proposed by Yamamura et al. for Al(III), Co(II), and Tb(III).
Main Results:
- Metals exhibited site preference: Co(II) and Al(III) preferentially bound to the N-site, while Tb(III) preferentially bound to the C-site.
- Positive cooperativity was observed for Fe(III) binding, whereas Co(II) and Tb(III) binding showed no cooperativity.
- Negative cooperativity was observed for Al(III) binding, with a binding constant ratio (KC/KN) of 0.12 ± 0.02 and a stacking coefficient (Kst) of 0.55 ± 0.22.
Conclusions:
- Chicken ovotransferrin displays differential selectivity for metal ions across its N and C terminal binding sites.
- The binding cooperativity varies significantly among different metal ions, with Al(III) exhibiting unique negative cooperativity.