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

AUTOR(ES)

Damadian, Raymond

RESUMO

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.

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