[Pterins: pigments, cofactors and signal connections in cell interactions].

Pteridines were originally described as pigments of insects and lower vertebrates. The electron-donating function of tetrahydrobiopterin for aromatic amino acid hydroxylation and thus, for neurotransmitter biosynthesis adduced the participation of unconjugated pterins in cellular metabolism. There has been increasing evidence moreover that they are signal molecules for intercellular recognition in primitive eucaryotes, as well as modifiers of signal polypeptides in higher vertebrates.