Amino Acid Transport in Mycoplasma

The uptake ofl -histidine byMycoplasma fermentans andl -methionine byM. hominis was found to be dependent on temperature andp H and to follow saturation kinetics. Several metabolic inhibitors inhibited this uptake. The transport system forl -methionine was highly specific. Thel -histidine transport system was less specific, and the uptake was competitively inhibited byl -arginine andl -lysine.l -Histidine accumulated in the intracellular pool ofM. fermentans at a concentration about 200 times that found in the medium. Efflux of accumulatedl -histidine was demonstrated at 37 C, but not at 0 C. The rate of efflux was greatly accelerated by addition ofl -histidine to the medium. The findings indicate that theMycoplasma cell membrane contains specific transport systems resembling the permease systems of other microorganisms.