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Active Transport of D-Alanine and Related Amino Acids by Whole Cells of Bacillus subtilis

¹ Department of Microbiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642

ABSTRACT

Whole cells of Bacillus subtilis transported D-alanine and L-alanine by two different systems. The high-affinity system (K_m of 1 µM and V_max of 0.6 to 0.8 nmol/min per mg of protein) was specific for the two stereoisomers of alanine. The low-affinity system (K_m of 10 µM for L-alanine and 20 µM for D-alanine and glycine) had a V_max of 5 to 12 nmol/min per mg of protein. This system transported glycine, D-cycloserine, and D-serine, in addition to D- and L-alanine. Azide inhibited the uptake of these amino acids and caused the efflux of D-alanine from preloaded cells. These data suggest that transport of these amino acids is energized by the electron transport chain.