Ion Metabolism in a Potassium Accumulation Mutant of Escherichia coli B I. Potassium Metabolism

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Abstract
A K transport mutant of E. coli is described which is deficient in the intake of K. The pheno-type of this mutant is characterized by failure to grow in K-deficient medium, failure to accumulate K+ in K+-deficient medium, a steady state intracellular K+ that varies sigmoidally with the medium K+ concentration, a sigmoidally shaped rate-concentration curve and a curved reciprocal plot for net K+ uptake kinetics and a low steady-state flux of K associated with a reduced influx rate constant. The data are discussed in terms of the present day models of cation transport. These models have led to 4 possible explanations of the mutant''s phenotype: a selectivity reversal such that intracellular cation binding sites bind another cation instead of K+; a structural alteration of cation binding cell proteins so that K+ is bound by cooperative binding (sigmoid isotherm) instead of by simple adsorption (hyperbolic isotherm); conversion of an enzyme in intermediate metabolism that rate-limits K+uptake to an allosteric pro- tein; conversion of the carrier protein for K+ to an allosteric protein.

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