Scytonemin is a biological pigment

Biological pigment

Biological pigments, also known simply as pigments or biochromes are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments...

 synthesized by many strains of cyanobacteria, including Calothrix sp., Lyngbya aestuarii, and others. It was originally discovered in 1849, although the structure remained unsolved until 1993. Scytonemin is believed to act as a bacterial sunscreen

Sunscreen

Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

 with a broad absorption from 325-425 nm and a separate maxima at 250 nm, and its biosynthesis

Biosynthesis

Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...

 triggered by exposure to UV light.

Biosynthesis

The biosynthesis in Lyngbya aestuarii was recently explored by Balskus, Case, and Walsh. It proceeds by the conversion of L-tryptophan to 3-indole pyruvic acid, followed by coupling to p-hydroxyphenylpyruvic acid. Cyclization of the resultant β-ketoacid yields a tricyclic ketone. Oxidation and dimerization yields the completed natural product. Three scytonemin biosynthetic enzymes are necessary, denoted as ScyA-C.