pHTomato is a pH-sensitive red fluorescent protein (FBrf0227962). It has similar dynamics to those seen in pHluorinE, with a pKa (close to 7.8) that is specifically tuned to report vesicle exocytosis. It contains six amino acid differences relative to mStraw (F41T, F83L, S182K, I194K, V195T and G196D) and has excitation (550 nm) and emission (580 nm) peaks similar to tdTomato (PMID:22634730).