Structural and stereoelectronic insights into oxygenase catalyzed formation of ethylene from 2-oxoglutarate

Ethylene is important in industry and biological signaling. In plants, ethylene is produced by oxidation of 1-aminocyclopropane-1-carboxylic acid, as catalyzed by 1- aminocyclopropane-1-carboxylic acid oxidase. Bacteria catalyze ethylene production, but via the four electron oxidation of 2-oxoglutarate to give ethylene in an arginine dependent reaction. Crystallographic and biochemical studies on the Pseudomonas syringae ethylene-forming enzyme reveal a branched mechanism. In one branch, an apparently typical 2-oxoglutarate oxygenase reaction to give succinate, carbon dioxide and, sometimes, pyrroline-5-carboxylate occurs. Alternatively, Grob-type oxidative fragmentation of a 2-oxoglutarate derived intermediate occurs to give ethylene and carbon dioxide. Crystallographic and quantum chemical studies reveal that fragmentation to give ethylene is promoted by binding of L-arginine in a non-oxidized conformation and of 2-oxoglutarate in an unprecedented high-energy conformation that favors ethylene rather than succinate formation