Asparagine transport in Lactobacillus plantarum and Streptococcus faecalis

The properties of het asparagine transport systems in Lactobacillus plantarum and Streptococcus faecalis are described. In both organisms the uptake of isotopically labeled l-asparagine was markedly stimulated by glucose. Kinetic studies yielded curvilinear Lineweaver-Burk plots in both organisms. These data were most consistently accounted for in both organisms by assuming the operation of two catalytic uptake components in addition to a diffusion component. The occasional limitation of kinetic studies in distinguishing between single or multiple catalytic components is illustrated. A large selection of structurally related amino acids and other substances were tested as competitors in initial rate studies. In L. plantarum the most effective competitors. structurally related dicarboxylic acid amide derivatives were only moderately effective competitors. In contrast, the most effective competitors of l-arparagine uptake in S. faecalis were relatively small neutral amino acids such as l-alanine, l-serine. l-αaminobutyric acid, l-cysteine and l-methionine, suggesting that asparagine enters this organism by reaction with a catalyst having relatively unspecific structural discrimination among neutral amino acids. Both organisms rapidly converted a large proportion of the transported asparagine to aspartic acid. In S. faecalis, the deamidation of l-asparagine was shown to be relatively insensitive to inhibition by those amino acids which were most effective in reducing the asparagine entry rate.