O-geNOps are orange fluorescent probe for single cell NO• measurements
O-geNOps are a class of orange fluorescent genetically encoded sensor capable for specific detection of intracellular nitric oxide (NO•) dynamics either within the cytosol (O-geNOp) or mitochondria (mtO-geNOp). These constructs have been developed on the basis of orange fluorescent protein (OFP) that is conjugated with a NO•-binding domain of the Escherichia coli protein NorR. Upon NO• binding to functional O-geNOps the orange fluorescence intensity is immediately quenched. The NO•-dependent quenching effect correlates with the cellular NO• concentration. Fluorescence of O-geNOps rapidly and fully recovers in the absence of NO•. Hence, O-geNOps provide a highly specific real-time read-out of local NO• dynamics on the level of individual cells or organelles (mitochondria). The excitation and emission maxima of O-geNOps are at 551 nm and 565 nm, respectively. Standard optical filters optimized for imaging of OFP should be used. ΔO-geNOps are NO insensitive constructs that should be used as respective controls.