Action of Tyrocidin and Detergents in Liberating Amino-Acids from Bacterial Cells

Abstract

THE estimation of amino-acids by the amino-acid decarboxylase technique¹ provides a means for the investigation of the amino-acid content of the internal environment of bacterial cells. If 1 ml. of a thick washed suspension of S. fæcalis cells grown in casein digest medium is placed along with 1·5 ml. phosphate buffer pH 6·0 in the main cup of a Warburg manometer and 0·5 ml. lysine decarboxylase preparation tipped in from a side-bulb in the usual way, there is a small output of carbon dioxide of magnitude depending upon the degree of washing of the cells and corresponding to the amount of lysine carried down with and adsorbed on the surface of the cells (see curve labelled'intact cells'). If a further aliquot of cell suspension is treated in such a way as to disintegrate the cells, either by mechanical shaking with glass beads² or by immersion in a boiling water bath for 10 min., before the addition of the enzyme, the amount of lysine assayed increases markedly (curve labelled 'boiled cells'). The difference in the quantities of lysine measured with the intact cells and with the disintegrated cells corresponds to the lysine liberated from the internal environment by disruption of the cell-wall, through which the enzyme cannot pass. Investigation of the amount of such lysine contained in the internal environment of the cells shows that its concentration depends upon that existing in the external environment, the ratio of the internal to external concentration varying from 2–3 for external concentrations of the order 0·02 M to approximately 20 for external concentrations of the order 0·001 M.