MIOX is the enzyme myo-inositol oxygenase. It catalyzes the first committed step in the glucuronate-xylulose pathway, It is a di-iron oxygenase with a key role in inositol metabolism. The structure reveals a monomeric, single-domain protein with a mostly helical fold that is distantly related to the diverse HD domain superfamily. The structural core is of five alpha-helices that contribute six ligands, four His and two Asp, to the di-iron centre where the two iron atoms are bridged by a putative hydroxide ion and one of the Asp ligands. The substrate is myo-inositol is bound in a terminal substrate-binding mode to a di-iron cluster. Within the structure are two additional proteinous lids that cover and shield the enzyme's active site.