Arginine Transport and Metabolism in Osmotically Shocked and Unshocked Cells of Escherichia coli W

Abstract

Abstract Exogenously derived arginine is extensively metabolized by early stationary phase cells of Escherichia coli W. This metabolism is substantial even during exposure to the substrate for only 15 sec at room temperature; at 300 sec only about 15% of the intracellular pool radioactivity is found in arginine. The major route of exogenous arginine metabolism is via an amineoxyacetic acid-inhibitable arginine decarboxylase which leads to the production and accumulation of large amounts of agmatine and putrescine. Much smaller amounts of ornithine, citrulline, proline, and glutamate also accumulate intracellularly. Cold osmotic shock treatment of the cells decreases the relative extent of arginine metabolism via the decarboxylase and increases metabolism via the other pathway (pathways). The net result is that proportionately more arginine is found in shocked cell pools than in the corresponding control cells. In the presence of 4 x 10-3 m amineoxyacetic acid the bulk of the pool radioactivity is found in arginine. Thus, under these conditions the pool radioactivity is a measure of arginine transport. Cold osmotic shock treatment reduces the amount of arginine-derived radioactivity associated with the cell in the presence and absence of 4 x 10-1 m amineoxyacetic acid. The shock treatment also reduces the capacity of the cell to transport exogenous lysine and leucine but not proline. In the presence of amineoxyacetic acid, l-lysine is a poor inhibitor of arginine transport, while l-canavanine, which itself is not well accumulated by these cells, is a modest inhibitor. l-Arginine is a good inhibitor of lysine transport while l-canavanine is a modest inhibitor. These data support the thesis that arginine and lysine are not transported by identical systems in this organism. Since lysine previously has been found to inhibit arginine uptake, these observations further support the conclusion that arginine transport cannot be reliably studied in E. coli without utilizing inhibitors such as amineoxyacetic acid which greatly attenuate the extensive metabolism of this amino acid.