title: Properties of alpha-aminoisobutyric acid transport in a thermophilic microorganism.
abstract: Uptake of alpha-aminoisobutyric acid (AIB) by a leucine-tyrosine auxotroph of a thermophilic microorganism starved for leucine was studied. AIB was taken up by the cells against a substantial concentration gradient (300:1) and was present there in a free and unchanged form. Various energy inhibitors and sulfhydryl reagents strongly inhibited the accumulation of AIB. AIB uptake obeyed saturation kinetics, and the Lineweaver-Burk plot is characterized by a biphasic curve. AIB most probably shares a common transport system(s) with alanine, serine, and glycine. A mutant defective in l-alanine uptake was isolated by using the suicide effect due to accumulation of the tritiated substrate. The mutant also exhibited impaired transport activity towards AIB, glycine, and l-serine, but not to phenylalanine or valine. The transport of AIB, glycine, l-alanine, and l-serine was induced by d-alanine (5 x 10(-3) M) during growth in a succinate- and ammonia-containing medium. De novo protein synthesis was required for the induction of AIB transport; the induction was inhibited when growth occurred in glucose-containing media. The apparent differential rate of synthesis of the AIB transport system was decreased considerably in glucose-grown cells as compared to succinate-grown cells. A common genetic basis of either the regulatory or structural nature for the transport of AIB, alanine, glycine, and serine in a thermophilic microorganism is suggested.
mesh_terms: D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000621:Aminoisobutyric Acids / Q000378:metabolism*; D001386:Azides / Q000494:pharmacology; D001419:Bacteria / Q000254:growth & development / Q000378:metabolism*; D001693:Biological Transport, Active; D002250:Carbon Radioisotopes; D002854:Chromatography, Paper; D003470:Culture Media; D003486:Cyanides / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D006358:Hot Temperature; D007930:Leucine / Q000378:metabolism; D009154:Mutation; D013053:Spectrophotometry; D013386:Succinates / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014316:Tritium; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D001386:Azides; D002250:Carbon Radioisotopes; D003470:Culture Media; D003486:Cyanides; D004140:Dinitrophenols; D013386:Succinates; D013439:Sulfhydryl Reagents; D014316:Tritium; D014443:Tyrosine; D007930:Leucine; D005947:Glucose