J. Mayshak, O. Yoder, K. Beamer
1966
Citations
0
Influential Citations
14
Citations
Quality indicators
Journal
Archives of biochemistry and biophysics
Abstract
Abstract From growth studies with Leuconostoc mesenteroides , it was recognized that glycyl- l -leucine was less effective than l -leucine in promoting growth when supplied as the sole source of l -leucine. A similar investigation had shown that glycyl- l -valine was a much more effective source of valine than was l -valine for this organism. To investigate the basis for this difference, kinetic studies were made with nongrowing but actively respiring cell suspensions of L. mesenteroides . The rate of uptake of leucine was significantly greater from l -leucine than from glycyl- l -leucine. The apparent association constants, K , for the transport systems were 11.0 × 10 3 for l -leucine and 2.25 × 10 3 for glycyl- l -leucine. Subsequent kinetic studies with combinations of labeled and unlabeled amino acids and peptides showed that l -leucine inhibited the uptake of leucine from glycyl- l -leucine but by a type of inhibition other than competitive inhibition. Glycyl- l -leucine did not inhibit the uptake of l -leucine. The free amino acids, l -leucine and l -valine, were competitive inhibitors and were transported by a common system, but their affinities for the transport system were different. The dipeptides, glycyl- l -leucine and glycyl- l -valine, exhibited competitive inhibition and interacted with a common uptake system which had a different specificity than for the free amino acids. This difference in specificity was demonstrated by the absence of any interaction between glycyl- l -leucine and the free amino acid, l -valine; similarly, no interaction occurred between glycyl- l -valine and l -leucine. The transport system responsible for the uptake of the amino acids was independent of the one operative for the dipeptides. These uptake systems were energy dependent as shown by the need for an energy source such as glucose and by the effect of 2,4-dinitrophenol and monobromoacetate which inhibited the uptake.