Indican is a colourless

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

, soluble in water, naturally occurring in ''

Indigofera ''Indigofera'' is a large genus of over 750 species of flowering plants belonging to the pea family Fabaceae. They are widely distributed throughout the tropical and subtropical regions of the world. Description ''Indigofera'' is a varied genu ...

'' plants. It is a precursor of

indigo dye Indigo dye is an organic compound with a distinctive indigo, blue color. Indigo is a natural dye obtained from the leaves of some plants of the Indigofera#Uses, ''Indigofera'' genus, in particular ''Indigofera tinctoria''. Dye-bearing ''Indigofer ...

Chemical reactions

Indican is a

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...

. Its most significant reaction is

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of to yields β-D-

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

and

indoxyl In organic chemistry, indoxyl is a nitrogenous substance with the chemical formula: C8H7NO. Indoxyl is isomeric with oxindol and is obtained as an oily liquid. Preparation The Heumann indigo synthesis starts from anthranilic acid: : In natu ...

. Beta-glucosidase, a common enzyme, catalyzes this process. Because the hydrolysis is slow in the absence of the enzyme, indican can be viewed as a protected version of indoxyl. Once formed, the indoxyl is oxidized by atmospheric oxygen to give blue

. Since synthetic indigo is produced on a massive scale by chemical routes, i.e. 50,000 tons/y (2011), the prospect of a biological pathway is of practical interest.

Medical significance

Biosynthesis

A reaction, similar to that used to produce indigo dye, is seen in the normal population, who excrete small amounts of the chemical in their urine. Normal urine reacting to

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

does at times produce a bluish tinge. Tryptophan is first converted to

indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...

(which is excreted in faeces), then to indican by

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

in the gut. Indican, being water-soluble, is then excreted through the

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

. Following absorption from the gut,

is converted to ''3-hydroxy indole (

or indican)'' in the liver, where it is again then conjugated with

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

glucuronic acid Glucuronic acid (GCA, from ) is a uronic acid that was first isolated from urine (hence the name "uronic acid"). It is found in many natural gum, gums such as gum arabic ( 18%), xanthan, and kombucha tea and is important for the metabolism of ...

through normal

xenobiotic metabolism Xenobiotic metabolism (from the Greek xenos (Greek), xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal bi ...

pathways. It is then transported to the kidneys for excretion. The enzyme "indoxyl esterase" has been found in humans and is involved in another pathway of chemical reactions involving indoxyl.

Pathology

Individuals affected by blue diaper syndrome exhibit a defect in

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...

metabolism. Tryptophan is first converted to indole, then to indican by bacteria in the gut. Indican is then excreted into the urine and from there into the diaper where, upon exposure to air, it is oxidised by atmospheric oxygen to indigo blue dye. Indican interferes with many commercial procedures for measuring total bilirubinIndican interference with six commercial procedures for measuring total bilirubin - Poon and Hinberg 31 (1): 92 - Clinical Chemistry
/ref> which can be a problem for renal failure patients whose blood indican levels are raised. It can cause gastrointestinal symptoms in patients whose

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

absorption is reduced, as in Hartnup's disease, allowing for greater bacterial decomposition of the

and its conversion to indican.

References

{{Glycosides Indoles Glucosides Indigo dye production