pH-Dependent Transport of Malate in Vesicles of the Symbiosome Membrane from Broad Bean Root Nodules

Using preparations of vesicles of symbiosome membrane (SM) obtained from nitrogen-fixing nodules of broad beans (Vicia faba L.) as a model system, the ability of malate, when transported through it, to cause coupled with proton translocation with the formation of ∆рН was studied. It was shown that in the presence of malate, the mechanism of H⁺ transfer through the SM occurs against the concentration gradient and does not depend on the alternative mechanism of ∆pH generation as a result of the functioning of H⁺-ATPase. Based on the kinetic curves of ∆pH generation using the acridine orange indicator, a constant was calculated that characterizes the malate concentration at which half the ∆pH generation rate is reached: K_m = 1.3 ± 0.7 mM. Such values indicate the presence of stoichiometry, i.e. conjugation of malate and H⁺ transport. Other singly charged cations (K⁺, Na⁺, \({\text{NH}}_{4}^{ + }\) ) cannot replace the role of the proton and their participation is reduced to the dissipation of ∆pH due to the exchange with the proton electrically neutral. The need for optimal maintenance of the ∆pH value in situ for malate translocation through the SM is considered as a possible mechanism that ensures the coordination of the relationships between the partners of nitrogen-fixing symbiosis not only at the level of metabolites, but also through the circulation of H⁺.