Summary: Starved cells of accumulated Zn by two different processes. The first was a rapid, energy- and temperature-independent system that probably represented binding to the cell surface. The cells also possessed an energy-, pH-, and temperature-dependent system that was capable of accumulating much greater quantities of the cation than the binding process. The energy-dependent system was inhibited by KCN, NaHAsO, -chlorophenyl carbonylcyanide hydrazone, -ethylmaleimide, EDTA and diethylenetriaminepenta-acetic acid. The system was specific inasmuch as Ca, Cr, Mn, Co or Cu did not compete with, inhibit, or enhance the process. Zn uptake was inhibited by Cd. The system exhibited saturation kinetics with a half-saturation value of 1.3 μM and a maximum rate of 0.21 (nmol Zn) min (mg dry wt) at 30 °C. Zn uptake required intact membranes since only the binding process was observed in the presence of nystatin, toluene, or sodium dodecyl sulphate. Cells did not exchange recently accumulated Zn following the addition of a large excess of non-radioactive Zn. Similarly, cells pre-loaded with Zn did not lose the cation during starvation, and efflux did not occur when glucose and exogenous Zn were supplied after the starvation period. Efflux was only observed after the addition of toluene or nystatin, or when cells were heated to 100 °C. Cells fed a large quantity of Zn contained a protein fraction resembling animal cell metallothionein. In batch culture, cells of accumulated Zn only during the lag phase and the latter half of the exponential-growth phase.


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