EQUILIBRIUM-CONSTANTS FOR THE BINDING OF ALUMINUM TO HUMAN-SERUM TRANSFERRIN

The binding of aluminum to human serum transferrin in 0.10 M N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid and 5 mM sodium bicarbonate at pH 7.4 has been studied by difference ultraviolet spectrophotometry. Aluminum binding produces peaks at 240 and 288 nm that are characteristic of binding at the transferrin specific metal binding sites. The more intense peak at 240 nm has a molar absorptivity of 14800 ± 1600 M−1 cm−1 and has been used to determine two macroscopic aluminum binding constants of log K1* = 13.5 ± 0.2 and log K2* = 12.5 ± 0.3. Titrations of both forms of monoferric transferrin with Al3+ indicate that the larger K1* value is associated primarily with Al binding at the C-terminal site and the smaller K2* value is associated primarily with the N-terminal site. The Al–transferrin binding constants have been used to include transferrin in the equilibrium distribution of aluminum calculated by using a computer model of serum. This model has been used to evaluate the potential of several low molecular weight ligands for use in decorporation of aluminum. © 1990, American Chemical Society. All rights reserved.