[The uptake of zinc into the interior of Chlorella]

The uptake of labelled Zn by asynchronous Chlorella fusca was measured under conditions of optimum and minimum energy supply (light and air, or dark and nitrogen, respectively). Part of the Zn equilibrates rapidly with the medium, and soon after the uptake it can be washed out quickly with non-labelled Zn carrier solution; it is probably bound in the free space (cell wall). This component of the uptake is also observed with cells kept in minimum conditions, with dead cells and with isolated cell wall material.Under optimum conditions Zn is taken up strongly for long periods and cannot be washed out completely. The velocity of uptake depends on the Zn content of the cells, and follows saturation kinetics. The uptake has no influence on the efflux of preabsorbed Rb. The retained Zn is thought to be inside the cells. It may enter by way of a pump. However, an energy-independent path of entry, with a differnt temperature coefficient, is also observed. All uptake processes are influenced by Ca.Part of the labelled Zn is slowly removed from the interior of the cell on treatment with a solution of carrier Zn or EDTA. This loss does not depend on energy supply and may occur via the second pathway. Net loss of labelled Zn is also observed after the energy supply is turned off, without change of solution, but the loss can be compensated by a simultaneous increase in the external concentration of labelled Zn. The question is discussed whether the energy-dependent Zn uptake is an "active" process.