rxYFP is a yellow fluorescent protein which is redox-sensitive due to a pair of redox-active Cys residues (at positions 149 and 202). Formation of a disulfide bond between the two residues (oxidized state) results in a 2.2-fold reduction of the emission peak compared to the reduced state at pH7.0. This process is fully reversible. The spectra of the two redox states are essentially identical, with an excitation peak of 512nm and an emission peak of 523nm. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene (UniProtKB:P42212), derived by mutagenesis of YFP, and contains the following mutations relative to the wild-type GFP sequence: C48V, S65A, V68L, S72A, Q80R, N149C, M153V, T203Y, S202C, D234H. (PMID:11689426).