The nonribosomally produced hydroxamate siderophore coelichelin from Streptomyces coelicolor contains the nonproteinogenic amino acidsN5-hydroxyornithine and N5-hydroxyformylornithine that are important for iron assembly. The hydroxylation of the δ-amino group of L-ornithine is catalyzed by the flavin-dependent monooxygenase CchB. During the redox reaction nicotinamide adenine dinucleotide phosphate (NADPH) and molecular oxygen are consumed and flavin adenine dinucleotide (FAD) is needed as a cofactor. During this work the monooxygenase was biochemically characterized and it could be shown that the hydroxylation of L-ornithine is most likely the first step in the biosynthesis of the siderophore coelichelin.
