The mechanism of zinc uptake by cultured rat liver cells.
1. The initial rate of 65Zn uptake into cultured rat hepatocytes has been measured over a range of Zn2+ concentrations from 3 x 10(-10) M to 5 x 10(-6) M. Histidine and albumin were used to buffer Zn2+ ions at concentrations below 1 x 10(-6) M. 2. The results suggest there are two mechanisms for Zn2+ uptake; a high-affinity, saturable pathway, with a maximum velocity (Vmax) of 20-30 pmol (mg protein)-1 min-1 and a Michaelis-Menten constant (Km) of about 2 x 10(-9) M Zn2+ (with histidine), and a low-affinity, linear pathway, that only makes a significant contribution to Zn2+ uptake at Zn2+ concentrations above 1 x 10(-6) M. 3. Transport via the high-affinity pathway is dependent on the concentration of Zn2+ ions and not on the concentrations of Zn(2+)-ligand complexes, suggesting that Zn2+ is the transported species. 4. The affinity of the saturable pathway for Zn2+ is slightly lower in the presence of albumin, with a Km of about 1.3 x 10(-8) M. The reason for this is uncertain.
Taylor
J A
JA
Biomedical Sciences Division, King's College London, Strand.
Simons
T J
TJ
D000418:Albumins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010873:Pinocytosis; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D000418:Albumins; D002712:Chlorides; D008024:Ligands; D006639:Histidine; D012964:Sodium; D015032:Zinc