Biophysical Evidence for His57 as a Proton-Binding Site in the Mammalian Intestinal Transporter hPepT1

Purpose. The objective of this study was to provide direct evidence of the relative importance of the His57 residue present in transmembrane domain 2 (TMD 2) and the His121 residue in TMD 4 as proton-binding sites in human PepT1 (hPepT1) by using a novel mutagenesis approach.