Proton-coupled amino-acid transporter that transports oligopeptides of 2 to 4 amino acids with a preference for dipeptides. a dipeptide(out) + H(+)(out) = a dipeptide(in) + H(+)(in) H(+)(out) + N-acetylmuramyl-L-alanyl-D-isoglutamine(out) = H(+)(in) + N-acetylmuramyl-L-alanyl-D-isoglutamine(in) carnosine(out) + H(+)(out) = carnosine(in) + H(+)(in) glycyl-sarcosine(out) + H(+)(out) = glycyl-sarcosine(in) + H(+)(in) Optimum pH is 7.5. Expressed in kidney, brain and gut. Also expressed weakly in eye, gill and skeletal muscle. Detected at 1 to 7 days post-fertilization (dpf). Expressed in the forebrain and midbrain at 1 dpf, where it localizes to the ependymal cell layer of the dicephalic ventricle and midbrain ventricle. Expressed in the developing otic vesicle at 2-7 dpf, where it shows particularly strong expression in the epithelium of the semicircular canal projections. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.