Evidence for nucleotide-dependent passive H+ transport protein in the plasma membrane of barley roots
2003
Yamashita, K. | Mimura, T. | Shimazaki, K.
Plasma membranes were isolated from barley roots by two-phase partitioning, and octylglucoside-soluble and -insoluble fractions were obtained. The insoluble fractions were reconstituted into liposomes, and the plasma membrane H+-ATPase was shown to participate in MgATP-dependent H+ transport activity. The H+ transport was decreased when the octylglucoside-soluble fraction was reconstituted together with the insoluble fraction. The decrease was not due to inhibition of the H+-ATPase, but rather was likely due to the increased H+ leakage from the proteoliposome. The octylglucoside-soluble fraction was, therefore, reconstituted in the liposomes and the passive H+ transport was determined using the pH jump method. A pH gradient across the membranes was generated by the pH jump, and the gradient was found to be dissipated by passive H+ transport. The H+ transport required ATP, K+, and valinomycin. The H+-transport also occurred when ADP, AMP, GTP, or ATP-gamma-S was present instead of ATP, and did not occur when the octylglucoside-soluble fraction was boiled before the reconstitution. These findings suggest that nucleotide-dependent H+ transport protein is present in the plasma membrane of root cells.
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