| Abstract: | Mycoplasma gallisepticum cells were found to contain two different sugar transport systems, one for d-glucose and alpha-methyl-d-glucoside (alpha-MG) and the other for d-mannose and d-fructose. Both systems were noninducible, stereospecific, dependent on temperature and pH, 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 alpha-MG. Both transport systems thus meet the criteria of active transport. The exit of alpha-MG from the cells, like its entry, depended on temperature and was accelerated by energy supplied by the oxidizable d-mannose. d-Glucose accelerated alpha-MG exit, apparently by an exchange reaction. A method for measuring the intercellular space and intracellular free-water volume of Mycoplasma was devised, and several of its applications are described. |
