Fig. 3.

Proposed outline mechanism. Ethylene and succinate formation occur in the presence of l-Arg (Fig. 1). Variations are possible [e.g., fragmentation of the cyclic peroxide intermediate II to give ethylene (21)], but are less likely, given the prevalence of intermediates of type III in 2OG oxygenase catalysis. NOG (and by implication 2OG) and l-Arg were observed in two conformations correlating with different Asp191 binding modes (Fig. 2). Formation of the bidentate 2OG intermediate complex I is supported by spectroscopic work (21). Turnover of 2OG to succinate also occurs (Fig. 1); succinate can be released from III, possibly with subsequent formation of H₂O₂. Formation of P5C occurs at a lower level than ethylene/succinate formation, via reaction of an Fe(IV)=O species (III), with l-Arg C-5. The hydroxylated product (IV) fragments and condenses to form P5C (21).