Summary: The use of a continuous Percoll gradient in a procedure for the rapid isolation of bacteroid- containing vesicles from French bean nodules is described. The purified vesicles appeared to be free from contamination by naked bacteroids and plant mitochondria and suitable for physiological studies. The metabolite uptake activities of vesicles isolated by this method were compared with those of free bacteroids. Succinate was transported through both peribacteroid and bacteroid membranes: the K, values were 320 p. and 57 p, respectively. For glucose K, values were 142 p. for the peribacteroid membrane and 102 p. for the bacteroid membrane, indicating that glucose could act as an energy-yielding substrate in functioning nodules. Experiments with inhibitors showed the involvement of ATPases in these transport processes and suggested that a proton-motive force was probably associated with them. The regulatory role of the peribacteroid membrane in the movement of the metabolites from the plant cytosol to bacteroids was demonstrated by its impermeability to glutamate, aspartate, citrate and benzoate.


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