Periplasmic respiration

The unique periplasmic respiration for the oxidative fermentation of AAB is reminiscent of the hydrogen or iron respiration of some chemolithotrophs, and also some specific oxidative fermentation such as glucose oxidation, alcohol oxidation, or gluconate oxidation could be fotmd in some related oxidative bacteria of pseudomonads or enteric bacteria. Thus, in this chapter, it is described, including some speculation, how this unique oxidative fermentation is distributed within the microbial world, and how this system (specific periplasmic dehydrogenase or terminal ubiquinol oxidases) is evolved or acquired in AAB. 

These reactions are the terminal electron-transfer reactions during anaerobic respiration, the enzymes being part of a redox loop generating a proton-motive force capable of driving ATP synthesis. Periplasmic nitrate reductase (Nap) participates in cellular redox processes, aerobic denitrification, and nitrate scavenging. ... 

Flanagan, D. A., Gregory, L. G., Carter, J. P., Karakas-Sen, A., Itichardson, D. J., and Spiro, S. (1999). Detection of genes for periplasmic nitrate reductase in nitrate respiring bacteria and in community DNA. FEMS Microbiol. Lett 177, 26 i—210. 

In addition to the membrane-anchored enzymes that support anaerobic respiration, bacteria express a number of functionally, and structurally, distinct nitrate reductases related by the presence of an Mo[MGD]2 containing active site. PFV has demonstrated tunnel-diode behaviour from two of these the periplasmic Rhodobacter sphaeroides NapAB and the assimilatory Synechococcus elongatus NarB. In both cases preferential binding of nitrate to the Mo , over Mo , oxidation state provides an explanation for the catalytic voltammetry and this may prove to be a conserved feature of the catalytic cycle in these enzymes. 

Lu W-P, Kelly DP (1988b) Respiration-driven proton translocation in Thiobacillus versutus and the role of the periplasmic thiosulphate-oxidizing enzyme system. Arch Microbiol 149 297-302... 

DMSO reductases are common enzymes that catalyze the reduction (Equation (3)) of DMSO to DMS in bacteria and fungi that are present in the oceans and salt marshes. These enzymes are located in the periplasm and function in a respiratory chain that uses DMSO as the terminal electron acceptor and involves the transfer of two electrons from a cytochrome, to form DMS. The activity of these enzymes can be linked to photosynthesis, for which they serve as a terminal electron acceptor. Although DMSO respiration (AG= 92kJmol ) does not provide as much... 

There are two remaining systems for enzymatic changes in arsenicals, the periplasmic reduction of arsenate to arsenite as part of an oxyanion-coupled anaerobic respiration (16,68) (Chapter 13) and the coupled cleavage of carbon-arsenic bonds with oxidation to arsenate (7). These systems appear to be of major environmental concern in arsenic-containing settings, but they have not been approached by molecular genetics as yet. 

Dissimilatory nitrite reductase of denitrifying bacteria is usually a soluble enzyme and it has been difficult to ascribe a phosphorylative function associated with the conversion of nitrite to nitric oxide. However, the demonstration by Wood (1978) that the terminal reductase in nitrite respiration is located in the periplasm implies that electrons generated in the cytoplasm must traverse the cytoplasmic membrane to the periplasmic nitrite reduction site. This location would require proton pumping, thus facilitating phosphorylation by the chemiosmotic mechanism. 

Fig. 10.1 Schematic representation of ethanol respiration of acetic acid bacteria (AAB). Ethanol is oxidized in the periplasm by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which also donate electrons to an ubiquinol oxidase that in turn generates a proton motive force. Acetic acid produced outside the cell is easily passed through the phospholipid bilayer of the bacteria and releases a proton in the cell cytoplasm...

---