Gluconacetobacter diazotrophicus is a N₂-fixing bacterium endophyte from sugar cane. The oxidation of ethanol to acetic acid of this organism takes place in the periplasmic space, and this reaction is catalyzed by two membrane-bound enzymes complexes: the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (ALDH). We present strong evidence showing that the well-known membrane-bound Alcohol dehydrogenase (ADHa) of Ga. diazotrophicus is indeed a double function enzyme, which is able to use primary alcohols (C2–C6) and its respective aldehydes as alternate substrates. Moreover, the enzyme utilizes ethanol as a substrate in a reaction mechanism where this is subjected to a two-step oxidation process to produce acetic acid without releasing the acetaldehyde intermediary to the media. Moreover, we propose a mechanism that, under physiological conditions, might permit a massive conversion of ethanol to acetic acid, as usually occurs in the acetic acid bacteria, but without the transient accumulation of the highly toxic acetaldehyde.

A mechanistic study is presented of the oxidative dehydrogenation of the iron(iii) complex [Fe^IIIL³]³⁺,1, (L³= 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanonane) in ethanol in the presence of molecular oxygen.

The enzyme 6‐phosphogluconate dehydrogenase catalyzes the conversion of 6‐phosphogluconate to ribulose‐5‐phosphate. It represents an important reaction in the oxidative pentose phosphate pathway, producing a ribose precursor essential for nucleotide and nucleic acid synthesis. We succeeded, for the first time, to determine the three‐dimensional structure of this enzyme from an acetic acid bacterium,Gluconacetobacter diazotrophicus(Gd6PGD). ActiveGd6PGD, a homodimer (70 kDa), was present in both the soluble and the membrane fractions of the nitrogen‐fixing microorganism. TheGd6PGD belongs to the newly described subfamily of short‐chain (333 AA) 6PGDs, compared to the long‐chain subfamily (480 AA; e.g.,Ovis aries, Homo sapiens). The shorter amino acid sequence inGd6PGD induces the exposition of hydrophobic residues in the C‐terminal domain. This distinct structural feature is key for the protein to associate with the membrane. Furthermore, in terms of function, the short‐chain 6PGD seems to prefer NAD⁺over NADP⁺, delivering NADH to the membrane‐bound NADH dehydrogenase of the microorganisms required by the terminal oxidases to reduce dioxygen to water for energy conservation.Enzyme: ECnonbreakingspace1.1.1.343.Database: Structural data are available in PDB database under the accession number6VPB.