pHluorinR is a pH-sensitive fluorescent protein that displays a reversible excitation ratio change between pH7.5 and 5.5 with a response time of less than 20ms. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212), containing the mutations E132D, S147E, N149L, V163A, N164I, K166Q, I167V, R168H, S175G, S202H and L220F (PMID:9671304).