Sugar Transport in Mycoplasma gallisepticum

Mycoplasma gallisepticum cells were found to contain two different sugar transport systems, one ford -glucose and α-methyl-d -glucoside (α-MG) and the other ford -mannose andd -fructose. Both systems were noninducible, stereospecific, dependent on temperature andp H, and sensitive to sulfhydryl-blocking reagents. The rate of sugar uptake depended on its external concentration, obeying Michaelis-Menten kinetics. The sugar accumulated in the cells against a concentration gradient, and an energy requirement for accumulation was demonstrated with α-MG. Both transport systems thus meet the criteria of active transport. The exit of α-MG from the cells, like its entry, depended on temperature and was accelerated by energy supplied by the oxidizabled -mannose.d -Glucose accelerated α-MG exit, apparently by an exchange reaction. A method for measuring the intercellular space and intracellular free-water volume ofMycoplasma was devised, and several of its applications are described.