Factors controlling the uptake and retention of methionine and ethionine by Ehrlich ascites carcinoma cells.

In a previous study (l), nn-methionine was shown to be a competitive inhibitor of the uptake of glycine by Ehrlich ascites cells. The results obtained, however, could not give any indication as to whether glycine and methionine are transported by the same or different systems. This problem has recently been the object of further consideration by Paine and Heinz (a), who were also unable to provide an unequivocal answer to the problem. Considerations of specificity of inhibition by other amino acids, however, did lead Tenenhouse and Quastel (3) to conclude that separate systems are required for the transport of glycine and L-S-ethylcysteine. Previously Heinz and Walsh (4) had suggested that amino acids which inhibit the transport of a given amino acid should undergo exchange diffusion with that amino acid. L-Methionine and on-ethionine are known to be excellent inhibitors of glycine transport (5), but no evidence could be obtained for loss of glycine from ascites cells by exchange diffusion with m-methionine (1). Loss of metabolites from cells has previously been demonstrated by, for example, the work of Rosenberg and Wilbrandt (6) on the exchange between labeled and unlabeled glucose in red blood cells. The ability of other amino acids to undergo exchange diffusion with methionine or ethionine has now been investigated. As this work was in progress, some account of such exchange was reported by Paine and Heinz (2).