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Properties of -Aminoisobutyric Acid Transport in a Thermophilic Microorganism

Department of Bacteriology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

ABSTRACT

Uptake of -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.