Oxygen‐Independent Decarbonylation of Aldehydes by Cyanobacterial Aldehyde Decarbonylase: A New Reaction of Diiron Enzymes

Abstract

Einfach Wasser zugeben: Mit ihrer Struktur gehören cyanobakterielle Aldehyd‐Decarbonylasen zur Enzymfamilie der Nichthäm‐Dieisen‐Oxygenasen – allerdings katalysiert das Enzym, in einer Sauerstoff‐unabhängigen Reaktion, die Hydrolyse von aliphatischen Aldehyden zu Alkanen und Formiat (siehe Schema). Die ungewöhnliche und chemisch schwierige Reaktion läuft höchstwahrscheinlich unter Beteiligung freier Radikale ab.

Insights into Substrate and Metal Binding from the Crystal Structure of Cyanobacterial Aldehyde Deformylating Oxygenase with Substrate Bound

“…18,25 We compared the activity of cADO in catalyzing the deformylation of compound 1 ( 500 μM) and octadecanal (500 μM + 4% DMSO to improve solubility) using previously described assay conditions with NADH and PMS as the auxiliary reducing system. 25,26 cADO deformylated 1 to produce 1-(2-(2-ethoxyethoxy)ethoxy)decane at a rate 0.049 ± 0.002 min –1 , a rate only ∼2-fold slower than the deformylation of octadecanal to heptadecane under similar conditions.…”

“…These alkanes are derived from fatty acyl-CoA esters in a two-step biosynthetic pathway that involves a fatty-acyl-CoA reductase (FAR) that first converts the fatty acyl-CoA ester to the corresponding aldehyde. 10−13 Next, an aldehyde decarbonylase (AD) cleaves the C1–C2 (aldehyde carbon−α-carbon) bond of the aldehyde to generate an alkane and, depending upon the organism, CO, 14,15 CO 2 , 8,16 or HCO 2 H. 17,18 …”

“…Recently, however, a soluble version of AD was discovered in cyanobacteria, 5 which is referred to as either cADO 21 (cyanobacterial aldehyde deformylating oxygenase) or in earlier reports as cAD (cyanobacterial aldehyde decarbonylase). 5,17,18,22,23 Although the physiological role of cADO in cyanobacteria remains unknown, the amenability of the enzyme has stimulated significant interest in understanding its mechanism and its use in engineering new pathways to generate alkane-based biofuels.…”

“…Labeling studies have shown that the aldehyde proton is retained in formate 17,18 and that one of the oxygen atoms derives from molecular oxygen, 22 whereas the proton in the product alkane derives from the solvent. 17,18 Spectroscopic studies point to the initial formation of a diferric intermediate in the cADO catalyzed reaction.…”

“…17,18 Spectroscopic studies point to the initial formation of a diferric intermediate in the cADO catalyzed reaction. 24 Addition of a further electron to this complex is proposed to lead to its breakdown and scission of the C1–C2 bond.…”