Binding of Al by protein in plasma of patients on maintenance hemodialysis

Gel filtration of plasma from hemodialysis patients, with use of reagents and apparatus with carefully minimized background Al concentrations, reproducibly showed a single peak for Al, corresponding exactly to the elution position of transferrin. The Al/transferrin molar ratio in adjacent fractions was constant (mean 0.126, SE 0.006) in replicate experiments. In contrast, the association of Al with albumin varied. Using both equilibrium dialysis and gel-filtration techniques, in the presence and absence of calcium or phosphate, we could demonstrate no significant binding of Al by human albumin at Al concentrations of 1 to 12 mumol/L. We saw no Al peak in pooled, concentrated, low-molecular-mass fractions of plasma gel-filtered on Sephadex G-50. Evidently, transferrin is the sole Al-binding protein in plasma of hemodialysis patients.