retinene

Nevertheless in that period, after dissecting retinas from 300 frogs, he found that rhodopsin on stimulation with light yielded both the protein opsin and a compound he called "retinene" (now "retinaldehyde") that in turn yielded vitamin A (now called retinol).

The Nobel Prize and the Discovery of Vitamins 2004

Retinene can exist in two forms, different in molecular shape, called cis-retinene and trans-retinene.

The Human Brain Asimov, Isaac 1963

In the dark, trans-retinene changes into cis-retinene and joins opsin once more to form the rhodopsin.

The Human Brain Asimov, Isaac 1963

If the diet is deficient in vitamin A, the body's stores eventually give out and retinene is not replaced as it is lost.

The Human Brain Asimov, Isaac 1963

Vitamin A, which is more stable, is, however, easily converted into retinene, so that the vitamin A stores of the body can be called upon to replace the constant dribbling loss of this visual pigment.

The Human Brain Asimov, Isaac 1963

In the presence of light, cis-retinene is converted to trans-retinene and, if it already makes up part of the rhodopsin molecule, it falls off, leaving the largely colorless opsin behind.

The Human Brain Asimov, Isaac 1963

The shape of cis-retinene is such that it can combine with opsin to form rhodopsin, whereas trans-retinene cannot.

The Human Brain Asimov, Isaac 1963