Cyanobacterial aldehyde decarbonylase (AD) catalyzes conversion of fatty aldehydes (R-CHO) to alka(e)nes (R-H) and formate. Curiously, although this reaction appears to be redox-neutral and formally hydrolytic, AD has a ferritin-like protein architecture and a carboxylate-bridged dimetal cofactor that are both structurally similar to those found in di-iron oxidases and oxygenases. In addition, the in vitro activity of the AD from Nostoc punctiforme (Np) was shown to require a reducing system similar to the systems employed by these O2-utilizing di-iron enzymes. Here, we resolve this conundrum by showing that aldehyde cleavage by the Np AD also requires dioxygen and results in incorporation of 18O from 18O2 into the formate product. AD thus oxygenates, without oxidizing, its substrate. We posit that (i) O2 adds to the reduced cofactor to generate a metal-bound peroxide nucleophile that attacks the substrate carbonyl and initiates a radical scission of the C1-C2 bond, and (ii) the reducing system delivers two electrons during aldehyde cleavage, ensuring a redox-neutral outcome, and two additional electrons to return an oxidized form of the cofactor back to the reduced, O2-reactive form.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry