Role of lithium ions in proline transport in Escherichia coli

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Abstract
Mechanisms of Li+ stimulation of proline transport were studied in cells of E. coli 7 and NR70, a mutant of strain 7 lacking ATPase (EC 3.6.1.3). An electrochemical potential difference of Li+ induced in an inward direction of energy-depleted cells caused a transient uptake of proline, depending on the driving force provided. When proline was added to unbuffered cell suspensions under anaerobic conditions, the medium was acidified only in the presence of Li+ but not in the presence of Na+ or K+. This acidification was abolished by the addition of a permeant anion. SCN-, to the medium containing Li+, but this was not demonstrated with cells of a mutant strain deficient in a carrier protein specific for proline. Proline is taken up by a mechanism of Li+ -proline cotransport in E. coli.