pHluorinE is a pH-sensitive green fluorescent protein. It gradually loses fluorescence as pH is lowered, until at pH values of less than 6.0, the excitation peak at 475nm vanishes. In an environment of pH less than 6.0, the protein is therefore invisible (eclipsed) under 475nm excitation, but can still be weakly seen at 395nm. These changes are reversible within less than 20ms after returning to neutral pH. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212), containing the mutations S147D, N149Q, T161I, V163A, S175G, S202F, Q204T and A206T (PMID:9671304).