In vitro expression of eel cone opsins. A. Expression of the eel sws2 opsin protein gave a calculated λmax of 445.6 ± 0.1 nm, in agreement with the previously measured λmax of 435 nm allowing for the differences in chromophores. B. Expression of the eel rh2 opsin protein gave a calculated λmax of 524.5 ± 0.0 nm, which is almost identical with the measured λmax of 525 nm. The close agreement between the MSP measurements and those of the in vitro expressed protein confirms that the isolated opsin sequences are those expressed by the cones.