ArnD is a deformylase involved in polymyxin resistance.

The modification of lipid A with cationic 4-amino-4-deoxy-l-arabinose residues serves to confer resistance against cationic peptide antibiotics in Gram-negative bacteria. In this work, the enzyme ArnD is shown to act as a metal-dependent deformylase in the biosynthesis of this carbohydrate.