The relative affinity of transferrin and albumin for zinc

The relative affinity of transferrin and albumin for zinc has been measured by competitive dialysis at a low zinc concentration in 0.15 M NaCl, 50 mM HEPES, 0.1 mM trisodium citrate (pH 7.2). There were small differences between albumins and larger ones between transferrin preparations, but all albumins bound zinc more firmly than any transferrin did. It is known that transferrin is largely responsible for the uptake of zinc from an intestinal membrane in rats, but much of the metal is subsequently transferred to albumin. The current results show that both in humans and in rats (a) no special mechanism is needed to provide energy for this transfer, and (b) full equilibration would lead to virtually complete transfer in contrast with what actually occurs in vivo.