Fig. 5. Basic principle of NOA-1.
NOA-1 represents a bipartite probe, which consist of the αsGC subunit fused to CGY, a FRET-based cGMP probe, and the βsGC subunit also fused to a CGY (upper panel). Upon NO binding to the βsGC-subunit the active heterodimeric sGC is formed and converts GTP into cGMP (middle panel). The NO-induced formation of cGMP is subsequently visualized with the FRET-based cGMP probe, named CGY (lower panel), which shows increased FRET in the presence of cGMP.