Magnesium transport in Escherichia coli.

Escherichia coli has a specitic active transport system for magnesium which can be studied with the radioisotope 28Mg. The accumulation of 2*Mg is temperature-dependent and inhibited by cyanide, dinitrophenol, and m-chlorophenyl carbonylcyanide hydrazone. The initial rate of uptake of SMg shows typical saturation kinetics with a & = 18 /LM magnesium and a V,,,,, = 0.56 pmole per min per 1012 cells at 25” ix$Tris medium. Neither calcium nor strontium compete with, inhibit, or stimulate the transport of 28Mg. However, manganese shows complex effects on celhrlar magnesium metabolism. (a) Manganese appears to be a competitive inhibitor for the magnesium accumulation system with a K; = 0.5 nm manganese in Tris. (b) The addition of high (5 to 10 m&r) manganese causes the rapid loss of *KMg from previously loaded cells and a net loss of magnesium, as if manganese were displacing internal bound magnesium which then leaves the cells via the magnesium transport system.