1.14.11.56 Co2+ exogenous Co2+ is coordinated by residues H106, H154, and D108. Co2+ is a mimic of the catalytic metal center because of its stability under aerobic conditions and its enzymatic inactivity under anaerobic conditions. The cis-face of the C4 carbon of L-Pro is properly oriented toward Co2+, which in nature exists as FeIV=O during the hydroxylation reaction, to generate the enantiopure cis-4-hydroxyproline 1.14.11.56 Fe2+ dependent on 1.14.11.56 Fe2+ Fe2+-dependent enzyme 1.14.11.56 Iron - 1.14.11.56 Iron presence of ferrous iron is required