Guanine is one of the five main nucleobases found in nucleic acids (e.g., DNA and RNA). Guanine is a purine derivative, and in Watson-Crick base pairing forms three hydrogen bonds with cytosine. Guanine "stacks" vertically with the other nucleobases via aromatic interactions. Guanine is a tautomer (see keto-enol tautomerism). The guanine nucleoside is called guanosine.
Guanine is also the name of a white amorphous substance found in the scales of certain fishes, the guano of sea-birds, and the liver and pancreas of mammals. In fact, the name of the nucleobase is derived from the term 'guano', because it was first isolated from bird manure.
In cosmetic industry, crystallic guanine is used as an additive to various products (eg. shampoos), where it provides the pearly iridescent effect. It provides shimmering lustre to eye shadow and nail polish. May irritate eyes. Its alternatives are synthetic pearl, and aluminium and bronze particles.
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