Under acidic conditions, in the presence of lysine, functions as a cadaverine:lysine antiporter that facilitates the excretion of cadaverine and the uptake of lysine (PubMed:1556085, PubMed:14982633). At neutral pH, also catalyzes the uptake of cadaverine via a proton symport mechanism, however the physiological relevance of this uptake activity is probably negligible because the expression of cadB is low at neutral pH (PubMed:14982633). Cadaverine uptake activity is low at acidic pH (PubMed:14982633). cadaverine(in) + L-lysine(out) = cadaverine(out) + L-lysine(in) cadaverine(in) + H(+)(in) = cadaverine(out) + H(+)(out) Uptake of cadaverine at neutral pH is greatly inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP), which dissipates the proton motive force, valinomycin, which dissipates the membrane potential, and nigericin, which dissipates the transmembrane pH gradient (PubMed:14982633). Cadaverine uptake at neutral pH is also inhibited by putrescine and lysine (PubMed:14982633). Cadaverine-lysine antiporter activity is not inhibited by CCCP (PubMed:14982633). Part of the cadB-cadA operon, which is under the control of the Pcad promoter (PubMed:1370290, PubMed:16491024). Expression is regulated by CadC (PubMed:1370290, PubMed:16491024). Highly expressed at acidic pH in the presence of lysine (PubMed:1370290, PubMed:16491024, PubMed:14982633). The global regulator Lrp has also a positive effect on the expression of the cadBA operon when cells are exposed to moderate acidic stress in the presence of lysine (PubMed:21441513). Repressed by H-NS under non-inducing conditions (PubMed:16491024). Repressed at pH 5.6 by OmpR (PubMed:29138484). Amino acid residues involved in both uptake and excretion, or solely in excretion, are located in the cytoplasmic loops and the cytoplasmic side of transmembrane segments, whereas residues involved in uptake are located in the periplasmic loops and the transmembrane segments. The SH-group of Cys-370 seems to be important for both uptake and excretion and may be necessary for recognition of the NH(2)-group of cadaverine. Mutant shows reduced amount of cadaverine in the medium. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Basic amino acid/polyamine antiporter (APA) (TC 2.A.3.2) family.