FIGURE 4.
In vitro characterization of CBS surface charge mutants of OpuA in hybrid membranes. Membrane vesicles of L. lactis bearing OpuA mutants were fused with liposomes composed of 50 mol % DOPE, 12 mol % DOPC, and 38 mol % DOPG. The ATP-regenerating system was enclosed inside the hybrid membranes. Uptake of [14C]glycine betaine by parental OpuA (•), OpuA[K1] (○), OpuA[K2] (▴), and OpuA[K2R] (▵) in hybrid membranes was assayed in 90 mm potassium Pi, pH 7.0, with or without added KCl as indicated on the x axis. Activation profiles in A show the measured values, whereas activation profiles in B represent normalized rates; data were normalized relative to the highest activity in the concentration range of 0 to 0.3 m KCl.