Cadmium uptake in Escherichia coli K-12

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Abstract
109Cd2+ uptake by E. coli occurred by means of an active transport system which has a Km of 2.1 .mu.M Cd2+ and a Vmax of 0.83 .mu.mol/min .cntdot. g (dry wt) in uptake buffer. 109Cd2+ accumulation was both energy dependent and temperature sensitive. The addition of 20 .mu.M Cd2+ or Zn2+ (but not Mn2+) to the cell suspensions preloaded with 109Cd2+ caused the exchange of Cd2+. 109Cd2+ (0.1 .mu.M) uptake by cells was inhibited by the addition of 20 .mu.M Zn2+ but not Mn2+. Zn2+ was a competitive inhibitor of 109Cd2+ uptake with an apparent Ki of 4.6 .mu.M Zn2+. Although Mn2+ did not inhibit 109Cd2+ uptake, the addition of either 20 .mu.M Cd2+ or Zn2+ prevented the uptake of 0.1 .mu.M 54Mn2+, which apparently occurs by a separate transport system. The inhibition of 54Mn2+ accumulation of Cd2+ or Zn2+ did not follow Michaelis-Menten kinetics and had no defined Ki values. Co2+ was a competitive inhibitor of Mn2+ uptake with an apparent Ki of 34 .mu.M Co2+. It was not possible to demonstrate an active transport system for 65Zn2+ in E. coli.