The rhodopsins of insects and other invertebrates differ from vertebrate rhodopsins on the point of the chemical events that follow the isomerization step. Vertebrate rhodopsins go through a series of spectrally distinct intermediates. The process is called bleaching because the absorption shifts from visible to ultraviolet wavelengths, which we can not see. The vertebrate process can lead to hydrolysis of the opsin and chromophore. Invertebrate rhodopsins generally do not bleach.
Light transforms the rhodopsins to a stable intermediate.
The isomerized 11- cis chromophore stays in place in the microvilli. The stable intermediates have spectral properties similar to metarhodopsin I of vertebrates, which has earned them the term metarhodopsins. The mechanism of transducing light-induced chemical changes in rhodopsins into electrical signals remains the major unresolved issue in understanding the physiology of light receptors. Several milliseconds are required before the absorption of light can be recorded as electrical activity in the receptor cell membrane. Certainly, the phototransduction event occurs during the transition from rhodopsin to metarhodopsin.