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). From Wordnik.com. [The Nobel Prize and the Discovery of Vitamins] Reference
retinene can exist in two forms, different in molecular shape, called cis-retinene and trans-retinene. From Wordnik.com. [The Human Brain]
In the dark, trans-retinene changes into cis-retinene and joins opsin once more to form the rhodopsin. From Wordnik.com. [The Human Brain]
The shape of cis-retinene is such that it can combine with opsin to form rhodopsin, whereas trans-retinene cannot. From Wordnik.com. [The Human Brain]
If the diet is deficient in vitamin A, the body's stores eventually give out and retinene is not replaced as it is lost. From Wordnik.com. [The Human Brain]
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. From Wordnik.com. [The Human Brain]
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. From Wordnik.com. [The Human Brain]
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