Activation of Acetone and Other Simple Ketones in Anaerobic Bacteria

Abstract

Acetone and other ketones are activated for subsequent degradation through carboxylation by many nitrate-reducing, phototrophic, and obligately aerobic bacteria. Acetone carboxylation leads to acetoacetate, which is subsequently activated to a thioester and degraded via thiolysis. Two different types of acetone carboxylases have been described, which require either 2 or 4 ATP equivalents as an energy supply for the carboxylation reaction. Both enzymes appear to combine acetone enolphosphate with carbonic phosphate to form acetoacetate. A similar but more complex enzyme is known to carboxylate the aromatic ketone acetophenone, a metabolic intermediate in anaerobic ethylbenzene metabolism in denitrifying bacteria, with simultaneous hydrolysis of 2 ATP to 2 ADP. Obligately anaerobic sulfate-reducing bacteria activate acetone to a four-carbon compound as well, but via a different process than bicarbonate- or CO₂-dependent carboxylation. The present evidence indicates that either carbon monoxide or a formyl residue is used as a cosubstrate, and that the overall ATP expenditure of this pathway is substantially lower than in the known acetone carboxylase reactions.

Anaerobic Microbial Degradation of Hydrocarbons: From Enzymatic Reactions to the Environment

“…The current knowledge on the activation of acetone and acetophenone by different types of carboxylases from sulfate-and nitrate-reducing bacteria is summarized by Heider et al [2016a]. Acetone carboxylase (Acx) from denitrifying A. aromaticum EbN1 and related enzymes from other organisms are heterohexameric (αβγ) 2 enzyme complexes which do not contain biotin, but 2-3 metal ions per (αβγ) 2 complex.…”

Optically Active 1‐Deuterio‐1‐phenylethane – Preparation and Proof of Enantiopurity

“…[10] The current perception of the reaction mechanism involves the formation of an intermediate carbocation. [11] However, it is unclear whether the reaction proceeds with retention, inversion or racemization at the methylene group of ethylbenzene. In particular, racemization would hint at the occurrence of a free carbenium ion in the transition state.…”

Synthesis of short-chain hydroxyaldehydes and their 2,4-dinitrophenylhydrazone derivatives, and separation of their isomers by high-performance liquid chromatography

“…In a non-aqueous system, separation of butyraldehyde and isobutyraldehyde was achieved with hexane as an eluent, but this protocol is not applicable to biological samples with their variable water content [8]. As possible intermediates of acetone degradation by sulfate-reducing bacteria, the determination of 2-hydroxyisobutyraldehyde, 3-hydroxybutyraldehyde and acetoacetaldehyde turned out to be essential for the elucidation of a proposed biochemical pathway [9,10]. No method for the analytical separation and quantification of these hydroxyaldehydes has been described in the literature.…”