Terms specific to pharmacology and retinoid transport

The chemistry of the chromophores of vision are closely tied to the chemistry of natural dyes and the field of pharmacology where many of these materials were first isolated. The following classes describe the relevant terms. 

Active-A term originally used to indicate whether a given retinoid showed biological activity as a vitamin in humans. More properly used to describe such activity in any species, order or phylum. 

Carotene-A hydrocarbon consisting of a conjugated carbon chain attached to an ionone ring. Most frequently, a conjugated carbon chain terminated at each end with an ionone ring. 

Protovitamin-A material, usually a dimer, that can be cleaved to produce one or more materials exhibiting biological activity associated with vitamins. 

Retinoid-A term undergoing nearly continual modification in order to accurately describe the characteristics of a large family derived from the carotenes and xanthophylls. The family exhibits specific properties required in vision, metabolism and reproduction. Many of these properties are dependent on the stereo-chemistry of the materials. Only some of the stereo-chemical features may be required in a given application. The definition of Spom, et. al. in 1994 is the most widely used. However, it does not stress the visual properties required to form a chromophore in vision. 

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