Solving the greenhouse gas riddle

A team of UK researchers has helped uncover the mystery of exactly how soil bacteria catalyse the reduction of nitrous oxide, N₂O, to nitrogen gas.  

N₂O is an important greenhouse gas which contributes to global warming. Experiments designed to understand how it is released into the atmosphere have gathered pace in recent years. 

N₂O reduction is the final stage in the denitrification process that converts soluble nitrate ions derived from artificial fertilisers into N₂. An enzyme found in soil bacteria called nitrous oxide reductase (N₂OR) catalyses the reduction of N₂O to N₂. The active site of N₂OR is a copper-sulfide cluster that forms a complex with N₂O. During the reduction process, electrons from one enzyme molecule transfer to a copper-N₂O complex on another.  

N₂O reduction starts when one of the enzyme sites is fed electrons from an outside donor, in this case a molecule called cytochrome c (Cyt c).  

A team of investigators, led by Andrew Thomson at the University of East Anglia, measured the rates of electron transfer between Cyt c and the active site of N₂OR to help understand the precise reduction mechanism.  

Thomson discovered that the transfer of electrons from Cyt c to the enzyme pair takes place only after a short time lag.  

The time delay can be explained by a small but important structural change that happens when Cyt c approaches the enzyme pair. Without this structural change, electron transfer is not possible and the reduction of N₂O slows dramatically.  

The model is still hypothetical, but Thomson thinks it might help solve the riddle of why N₂OR reduces N₂O in such a controlled manner. 

Gaetano Mancino