title: Transport of alpha-aminoisobutyric acid by Streptococcus pyogenes and its derived L-form.
abstract: We studied the uptake of alpha-aminoisobutyric acid (AIB) in Streptococcus pyogenes and its physiologically isotonic L-form. S. pyogenes cells starved for glucose or treated with carbonyl cyanide-m-chlorophenyl hydrazone accumulated limited amounts of AIB. A high apparent K(m) value characterized the glucose-independent transport of AIB. The rate and extent of AIB accumulation significantly increased in the presence of glucose. Two saturable transport components with distinct apparent K(m) values characterized glycolysis-coupled transport of AIB. A biphasic Lineweaver-Burk plot was also obtained for l-alanine transport by glycolyzing S. pyogenes cells. AIB seems to share a common transport system(s) with glycine, l- and d-alanine, l-serine, and l-valine. This was shown by the competitive inhibition of AIB uptake by these compounds and their ability to induce competitive exchange efflux of accumulated AIB. About 30% of the AIB uptake was not inhibited by a saturating amount of l-valine, indicating the existence of more than one system for AIB transport. p-Chloromercuribenzoate markedly inhibited the accumulation of AIB by both glycolyzing and glucose-starved cells. In contrast, carbonyl cyanide-m-chlorophenyl hydrazone affected only metabolism-dependent uptake of AIB, which was also sensitive to dinitrophenol, N-ethylmaleimide, iodoacetate, fluoride (NaF), arsenate, and N,N'-dicyclohexylcarbodiimide. These results are interpreted according to the chemiosmotic theory of Mitchell, whereby a proton motive force constitutes the driving force for AIB accumulation. AIB was not accumulated by the L-form. However, a temporary accumulation of AIB by a counterflow mechanism and a saturable system with a low apparent affinity were demonstrated for AIB transport by this organism. We suggest that a deficiency in the coupling of energy to AIB transport is responsible for the apparent lack of active AIB accumulation by the L-form.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000621:Aminoisobutyric Acids / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002413:Cations, Divalent / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007740:L Forms / Q000378:metabolism*; D013297:Streptococcus pyogenes / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000621:Aminoisobutyric Acids; D002413:Cations, Divalent; D002414:Cations, Monovalent; D000409:Alanine