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

Abstract

A potassium transport mutant of Escherichia coli is described which is deficient in the intake of potassium. The phenotype of this mutant is characterized by (i) failure to grow in K + -deficient medium, (ii) failure to accumulate K + in K + -deficient medium, (iii) a steady-state intracellular K + that varies sigmoidally with the medium K + concentration, (iv) a signoidally shaped rate-concentration curve and a curved reciprocal plot for net K + uptake kinetics, and (v) a low steady-state flux of potassium 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 four possible explanations of the mutant's phenotype: (i) a selectivity reversal such that intracellular cation binding sites bind another cation instead of K + ; (ii) 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); (iii) conversion of an enzyme in intermediate metabolism that rate-limits K + uptake to an allosteric protein; (iv) conversion of the “carrier protein” for K + to an allosteric protein.