Enzymes oxygen-sensitive

CODH/ACS is an extremely oxygen-sensitive protein that has been found in anaerobic microbes. It also is one of the three known nickel iron-sulfur proteins. Some authors would consider that there are only two, since the CODH and ACS activities are tightly linked in many organisms. However, there is strong evidence that the ACS and CODH activities are associated with different protein subunits and the reactions that the two enzymes catalyze are quite different. CODH catalyzes a redox reaction and ACS catalyzes the nonredox condensation of a methyl group, a carbonyl group, and an organic thiol (coenzyme A). 

The occurrence of 3,4-dihydroxybenzoate decarboxylase was also found widely in facultative anaerobes. Among them, Enterobacter cloacae P241 showed the highest activity of 3,4-hydroxybenzoate decarboxylase, and the activity of the cell-free extract of E. cloacae P241 was determined to be 0.629 p.mol min (mg protein) at 30°C, which was more than that of C. hydroxybenzoicum, 0.11 (xmol min mg protein)" at 25°C. The E. cloacae P241 enzyme has a molecular mass of 334 kDa and consists of six identical 50 kDa subunits. The value for 3,4-dihydroxybenzoate was 177 p.M. The enzyme is also characteristic of its narrow substrate specificity and does not act on 4-hydroxybenzoate and other benzoate derivatives. The properties of E. cloacae P241 3,4-hydroxybenzoate decarboxylase were similar to those of C. hydroxybenzoicum in optimum temperature and pH, oxygen sensitivity, and substrate specificity. 

The reversible decarboxylation of 4-hydroxybenzoate and 3,4-dihydroxybenzoate has been described in Sedimentibacter (Clostridium) hydroxybenzoicum (He and Wiegel 1996), and the oxygen-sensitive enzyme has been purified. The decarboxylase from Pantoae... 

Oxygen-sensitive samples such as enzymes from strictly anaerobic microorganisms which have been previously prepared anaerobically (e.g., in a glove box) can be transferred from their container (e.g., a capped septum bottle) to an empty EPR tube that has been made anaerobic on the manifold. The transfer can be done with an injection needle that has been made anaerobic in an empty septum bottle on the manifold. Note that after the transfer the connecting rubber has a hole, so any addition to this sample can only be made after it has been frozen and subsequently made anaerobic with a new, intact connecting rubber on the manifold. 

The enzyme involved in the degradation of the dyes has been shown to be azoreductase. The enzymes were first isolated from the intestinal microflora and was later found to be produced by the cytosolic and microsomal fractions of the liver [47]. The enzyme was sensitive to oxygen and was inactivated by oxygen. In experiments involving intestinal anaerobic bacteria, Rafii et al. found the requirement of... 

Anaerobic azo dye reduction can be mediated by enzymes, low molecular weight redox mediators, and chemical reduction by biogenic reductants. These reactions can be located either intracellular or extracellular. Reduction of highly polar azo dyes, which cannot pass through the cell membranes, is located outside the cell. Like azo dyes, nicotinamide adenine dinucleotide phosphate, which is believed to be the main source of electrons, also cannot pass through the cell membranes. Azo reductase enzyme, which is oxygen-sensitive and released extracellularly, is found to be responsible for the reduction of azo dyes. 

Another way to solve this problem is to prevent the enzyme in the fruit from acting as a catalyst. Enzymes are sensitive to pH. Therefore, adding an acid such as lemon juice or vinegar to fruit can prevent the enzyme from acting. You may have noticed that avocado salad recipes often include lemon juice. In addition to hindering the enzyme, lemon juice contains vitamin C, which is very reactive toward oxygen. The vitamin C reacts with oxygen before the sliced fruit can do so. 

Anaerobic glovebox used for purification of oxygen-sensitive enzymes... 

More recently, Pearce and Heydeman suggested non-oxidative removal of ethylene glycol units as acetaldehyde by a membrane-bound, oxygen-sensitive enzyme of a novel type, i.e., diethylene glycol lyase (18). Schoberl suggested that PEG was catabolized by Ci step, liberating formate which was metabolized by a serine pathway (19). 

This pathway involves oxygen-sensitive enzymes and electron carriers, and therefore is found in anaerobic or microaerobic bacteria, such as anaerobic sulfate reducers... 

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