MEMBRANE SPECIFICITY OF LEUCONOSTOC MESENTEROIDES FOR THE STEREOISOMERIC FORMS OF GLYCINE AND VALINE DIPEPTIDES

Abstract

Transport systems of Leuconostoc mesenteroides differ greatly in the stereochemical specificity exhibited for amino acids and dipeptides. Nongrowing cell suspensions of this organism accumulated D- and L-valine to approximately the same extent, whereas no measurable transport of valine from glycyl-D-valine occurred. In concurrent studies, however, a very high uptake of valine was found from glycyl-L-valine. Stereospecific synthesis of the various radioactive valine dipeptides permitted more extensive studies. No valine transport was found from any of the isomeric forms if D-valine was one of the amino acid moieties. Consistent with these observations, no hydrolysis of any dipeptide by intracellular dipeptidases could be detected when D-valine was a part of the peptide. This difference in stereochemical specificity supports the concept of separate transport sites for amino acids and related dipeptides.