Active transport of nonpolar amino acids in Chromatium vinosum.
The photosynthetic purple sulfur bacterium, Chromatium vinosum, takes up the amino acids, L-phenylalanine and L-leucine, via two apparently different electrogenic, H+/amino acid symports. Na+ serves as an allosteric modulator for leucine transport, lowering the Km for leucine from 66 to 15 microM. C. vinosum cells also contain a system that transports both isoleucine and valine. The isoleucine/valine system has the attributes of a H+/amino acid symport at pH less than 7.5 but appears to function as a H+/Na+ (Li+)/amino acid symport at pH greater than or equal to 7.5. Na+ gradients produce an allosteric lowering of the Km values for both isoleucine and valine, from 14 to 7 microM and from 34 to 17 microM, respectively. C. vinosum also accumulates D-alanine in an energy-dependent reaction. The transport process appears to involve the electrogenic cotransport of D-alanine and Na+. The Km value for D-alanine was determined to be 9 microM. Unlike the previously characterized C. vinosum L-alanine/Na+ symport, Na+ gradients did not affect the Km for D-alanine transport. L-Alanine and glycine, but not alpha-aminoisobutyric acid, act as competitive inhibitors for D-alanine transport.
D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D002844:Chromatium / Q000187:drug effects / Q000378:metabolism*; D003624:Darkness; D006863:Hydrogen-Ion Concentration; D007532:Isoleucine / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008027:Light; D010649:Phenylalanine / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D014633:Valine / Q000378:metabolism
D000596:Amino Acids; D007532:Isoleucine; D010649:Phenylalanine; D012964:Sodium; D007930:Leucine; D014633:Valine; D000409:Alanine