The reversible photoinduced structural changes of a green fluorescent protein (GFP) mutant and their optical control are reported. A photoreversible optically inactive configuration is demonstrated with the absorption peak at 365 nm. which is consistent with a photoisomerization pathway associated with hydrogen-bond breaking in the chromophore environment. We show that this state is involved in the switching dynamics recently discovered in these molecules and we determine the transition rates of the reversible photoconversion processes. These experiments combine to provide the framework for the implementation and optimization of efficient room-temperature GFP-based all-optical memories that use the fluorescent properties of these proteins.