Fig. 2. (A) Peptide-dependent Acridine Orange fluorescence quenching in icefish intestine brush-border membrane vesicles (BBMVs). In addition to valinomycin, the cuvettes contained 100 mmol l^-1 KCl (trace a); 100 mmol l^-1 KCl + 20 mmol l^-1 Gly-L-Pro (trace b); 100 mmol l^-1 choline chloride (trace c); 100 mmol l^-1 choline chloride + 20 mmol l^-1 Gly-L-Pro (trace d). (B) Effects of exogenous dipeptides on H⁺ influx rate (trace d — trace c, N=5). (C) Dependence of the initial rate of H⁺ influx on increasing extravesicular Gly-L-Pro concentrations. Inset, the Woolf—Augustinsson—Hofstee plot of the experimental data (N=3). (D) Diethylpyrocarbonate (DEP) inhibition of proton accumulation in icefish intestinal BBMVs (N=4). Values were significant at ^*P<0.05; ^**P<0.01.