Retinene

The retinenes (retinene₁ and retinene₂) are chemical derivatives of vitamin A (see retinol) formed through oxidation reactions.

Retinene₁ is better known as retinal and is fundamental in the transduction of light into visual signals in the photoreceptor level of the retina (known as the visual cycle). Retinene₂ is more formally known as dehydroretinal.

The energy of impinging photons will convert retinaldehyde from an 11-cis isomer into an all-trans form. In the retina, this conversion induces a conformational change in the surrounding opsin protein pigment, leading to signaling through the G protein transducin. Retinaldehyde also forms a part of bacteriorhodopsin, a light-induced proton pump found in some archaea.

Experimentally, it is possible to replace 11-cis retinaldehyde by perfusing retinal tissue preparations with retinaldehyde derivatives. Selective modification of the retinaldehyde structure, particularly the density of electrons in the π-orbitals, can lead to insights into the interaction between the retinaldehyde moiety and the surrounding pigment protein.

"The names of all these molecules have recently been changed ... vitamin A is now retinol, retinene is retinal; there is also retinoic acid"—George Wald (1967).¹