Trace element uptake in liver cells. 2. Effect of different proteins in the medium on the uptake of copper and zinc by hepatoma cells.
Cultured rat hepatoma cells (HTC-cells) were used to study the uptake of copper and zinc from a minimal salt-glucose medium, supplemented with albumin from different species or with ovalbumin. Competitive equilibrium dialysis showed that at low molar ratios of metal/protein (less than 1) the affinity for copper of human and bovine albumin was about equal, but that of dog albumin or ovalbumin was much lower. Only a small difference in affinity for zinc could be detected between human albumin and ovalbumin. Supplementing the medium with the different proteins the rate of copper uptake in the cell at a given molar Cu/protein ratio increased as follows: human albumin congruent to bovine albumin less than dog albumin less than ovalbumin. When the molar Cu/protein ratio was increased, a discontinuity was seen with all three albumin species at a ratio of about 1. In contrast, the zinc uptake mimics that of Cu/ovalbumin, and no discontinuity was observed using different molar Zn/protein ratios. These results indicate that the rate of copper and zinc uptake depends strongly on its affinity for the protein: a low affinity leads to a high uptake. The results suggest further that at physiologic concentrations zinc is taken up by a mechanism different from that for copper.
D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D003300:Copper / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism; D014131:Trace Elements / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*
D012709:Serum Albumin; D014131:Trace Elements; D003300:Copper; D015032:Zinc