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

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.