Estimation of the ferrous-transferrin binding constants based on thermodynamic studies of nickel(II)-transferrin

J Inorg Biochem. 1986 May;27(1):41-52. doi: 10.1016/0162-0134(86)80107-6.


The equilibrium constants for the binding of Ni2+ to human serum transferrin in 0.01 M hepes containing 5 mM sodium bicarbonate at 25 degrees C and pH 7.4 have been measured. The effective binding constants are log K1 = 4.10 +/- 0.15 and log K2 = 3.23 +/- 0.31 for the reactions Ni2+ + apoTr (K1) in equilibrium Ni2+-Tr. Ni2+ + Ni2+-Tr (K2) in equilibrium Ni2+-Tr-Ni2+ where the explicit terms for bicarbonate and hydrogen ion have been incorporated into the effective binding constants. Titration of both forms of mono(ferric)transferrin indicates that unlike other metal ions, Ni2+ binds preferentially to the N-terminal binding site, but that the site preference is rather small. A linear-free-energy relationship (LFER) for the complexation of Ni2+ and Fe2+ has been prepared. This LFER has been used to estimate effective binding constants of log K1 = 3.2 and log K2 = 2.5 for the ferrous-transferrin complex. These ferrous constants have been combined with the literature binding constants for ferric-transferrin to estimate formal reduction potentials of -340 mV vs. NHE for the C-terminal site and -280 mV for the N-terminal site.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Humans
  • Iron / metabolism*
  • Kinetics
  • Nickel / metabolism*
  • Protein Binding
  • Spectrophotometry, Ultraviolet
  • Thermodynamics
  • Transferrin / metabolism*


  • Transferrin
  • nickel chloride
  • Nickel
  • Iron