Formaldehyde Dehydrogenase

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Formaldehyde dehydrogenase (FADH) is a member of the medium zinc chain alcohol dehydrogenase family. It exists in most prokaryotes and all eukaryotes. It is an enzyme mainly used for formaldehyde detoxification in microorganisms. In recent years, some studies have determined that formaldehyde dehydrogenase also has the activity of S-nitrosoglutathione reductase (GSNOR), which is used to regulate the dynamic balance of endogenous NO.

Figure 1. Structure of formaldehyde dehydrogenase.

Introductions

Formaldehyde is an active compound that can react non-specifically with proteins, nucleic acids and lipids, and is highly toxic to all organisms. The source of formaldehyde is very wide. In order to prevent the lethal and mutagenic effects of formaldehyde on organisms, organisms have established a variety of repair mechanisms to enable them to survive better in an environment containing formaldehyde. Among them, the oxidation pathway of formaldehyde is widespread in microorganisms. A way of detoxification. The key enzyme formaldehyde dehydrogenase that acts on this pathway is a member of the medium zinc chain alcohol dehydrogenase family. It exists in most prokaryotes and all eukaryotes, and plays an important role in the detoxification of microbial formaldehyde. In recent years, more and more studies have shown that FADH is not only used for the detoxification of formaldehyde, but also has some connection with NO metabolism, showing S-nitrosoglutathione reductase activity.

Physiological role of formaldehyde dehydrogenase

• Detoxification of formaldehyde

One of the main functions of FADH in microorganisms is the detoxification of formaldehyde, and the formaldehyde oxidation pathway is a widespread enzymatic system in the conversion of formaldehyde. Most FADH usually requires NAD+ and glutathione (GSH) to participate in the oxidation of formaldehyde. Formaldehyde dehydrogenase (PFADH) in Pseudomonas putida is the only enzyme that can oxidize formaldehyde without the participation of GSH.

• Regulate the dynamic balance of endogenous NO

NO is a signal molecule involving many functions in the organism. NO-derived reactive nitrogen species (RNS) can easily form S-nitrosoglutathione (GSNO) with the main intracellular antioxidant GSH. GSNO biotransformation is the main branch of NO metabolism, and endogenous GSNO is an important factor in the regulation of NO homeostasis.

Biochemical properties

• Substrate preference

Many studies have shown that GSH-FADH from different biological sources has high activity on long-chain alcohols such as n-octanol, GSH adducts such as HMGSH, GSNO and other large substrates, while for some small alcohols, it has only Very low or no activity.

• Stability

FADH has good thermal stability, and the optimum temperature is 30°C.

• Kinetic reaction mechanism

The reaction of FADH follows a random ping-pong kinetic mechanism, in which a reductive and oxidative initial complex is produced during the process of random ping-pong kinetics. The binding of the coenzyme during the reaction makes the catalytic domain of the enzyme rotate 10 degrees to the coenzyme-binding domain, and the active site becomes narrower, making the enzyme reach an optimal position in binding small molecule substrates.

Structure of formaldehyde dehydrogenase

SDS-PAGE analysis revealed that the molecular weights of FADH subunits were all around 40 kD, and gel filtration chromatography showed that there were dimers and tetramers. Studies have found that the formaldehyde dehydrogenases in Escherichia coli and Rhodobacter sphaeroides are usually dimeric proteins, while Pseudomonas putida, Paracoccus denitrificans, yeasts and Sulfolobus sulphureus are in the form of tetramers. The monomer structure of GSH-dependent FADH is basically similar whether it is dimer or tetramer, while GSH-independent FADH has a different structure.

FADH gene expression regulation

The transcription of FADH-encoding genes can be activated by intermediates accumulated in the process of formaldehyde metabolism and signal molecules generated by reducing power in the pathway. Studies have found that Escherichia coli and Haemophilus influenzae can induce the production of FADH enzyme activity at a formaldehyde concentration of 0.6-20 ppm; at the same time, it has also been found in the gram-negative bacteria Paracoccus denitrificans, when its growth substrate is one carbon Compounds can induce the production of FADH enzyme activity, but not when the substrate is methanol or formic acid, indicating that FADH is inducible.

Applications

• Detection of the concentration of formaldehyde

Enzymatic detection of formaldehyde using the catalytic properties of formaldehyde dehydrogenase is not only low in cost but also simple in operation, suitable for daily use in workplaces.

• CO2 recycling

The enzymatic catalysis of CO2 to methanol requires the participation of formaldehyde dehydrogenase and two other key enzymes (formate dehydrogenase and alcohol dehydrogenase).

Conclusions

Formaldehyde dehydrogenase exists in most prokaryotes and all eukaryotes. Formaldehyde dehydrogenases from different sources show a high degree of sequence similarity. The conservative existence of formaldehyde dehydrogenase indicates its important role in organisms. The formaldehyde oxidation pathway of formaldehyde dehydrogenase action is a detoxification system widely existing in organisms.