FLAVINS & CRYPTOCHROMES
Flavins are a group of organic alkaloids based upon
IsoAlloxazine (a tricyclic alkaloid with a Pteridine core) the most well known of which is Riboflavin, a Flavin with a
Ribose sugar (more correctly a 'ribityl') moiety attached to the 'R' position. The Flavins are derived from Riboflavin.
[Pteridine itself is composed of two fused rings, one of
Pyrimidine the other of
Pyrazine, which are isomers of one another. Compare Pteridine with the Purines, which are bicyclic with 4 similar heterocyclic nitrogen atoms but where one of the rings is 5-sided].
The class of compounds called Pterins are also based upon Pyrazine rings and are very colourful compounds utilised by Butterflies as Butterfly Wing Dyes].
Riboflavin, which is also known as Vitamin B2, is essential to mammals and plays a key role in energy metabolism of fats, ketones, carbohydrates and proteins. Riboflavin is based upon Pteridine and is one of the Flavins. In solution is both coloured yellow and fluoresces yellow-green under ultraviolet light. In solid form it is more orange in colour.
Riboflavin occurs in the free form within the retina of the eye. It is also found in Legumes,Asparagus, Green Peas,
Spinach and in whole grains.
Flavins are those substances with the structures shown above, where the radical 'R' (shown in red) can be any group. Two forms exist, an oxidized form which is yellow in aqueous solution, and a reduced form with hydrogen atoms on either or both nitrogen atoms. If both nitrogen atoms have a hydrogen atom (as shown) then the Flavin is fully reduced and is now colourless. If only partially reduced with a hydrogen atom on either nitrogen atom, then it may be either red or blue, depending upon certain other factors.
An important role of Flavins within living things is that they chemically combine with proteins, the result called
Flavoproteins. One such Flavoprotein is
Cryptochrome 1 which is a Cryptochrome. Cryptochromes are a class of blue-light sensitive flavoproteins found in both plants and animals which play an important role in the regulation of circadian rhythms and in photomorphogenesis in Thale Cress. The cryptochrome within Thale Cress is also responsible for its phototropism (the flowers turning towards the sun), for its circadian rhythms and somewhat amazingly is also responsive to magnetic fields.
Cryptochromes change colour in response to either acidic conditions or by excitation with light (which frees an electron) where they undergo a change in oxidation similar to that observed in the Flavins. It is not possible to show the structure of Cryptochrome 1, for it has a very high molecular weight, consisting of about 500 amino acids and a flavin adenine dinucleotide. Cryptochrome 1 is known to have two chromophores; a Flavin and a Pterin in the specific form of
5,10-Methenyl-TetraHydroFolic Acid (or
MHF for short).
Other Flavoproteins mediate the phototropic response to light, where the plant moves in response to light.
Thale Cress, in response to blue light, transports Cryptochrome 1 into the cell nucleus where it instigates a change in turgor pressure and causes stem elongation. It is responsible for the blue-light stimulated growth of the leaves.
Of all of the substances depicted above, many of which are shown for comparison only, the only ones with a reported presence in Thale Cress are the Flavins and Cryptochrome 1.