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Aldehyde dehydrogenase: an overview

Published on 2/25/2019
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Acetaldehyde dehydrogenase, abbreviated as ALDH, a kind of aldehyde dehydrogenase, responsible for catalyzing the oxidation of acetaldehyde to acetic acid. The alcohol dehydrogenase in the liver is responsible for the oxidation of ethanol (the component of wine) to acetaldehyde. The aldehyde is further converted to a harmless acetic acid (i.e., a component of vinegar) as a substrate under the catalysis of acetaldehyde dehydrogenase.

CH3CHO + NAD + CoA → acetyl CoA + NADH + H It is known that human aldehyde dehydrogenase is encoded by three genes: ALDH1A1, ALDH2 and the recently discovered ALDH1B1 (also known as ALDH5).

 

Structure

Cysteine-302 is a nucleophile and is the active center of the enzyme. Both Cys residues in the cytosol and mitochondrial isozymes can react with the labeled iodoacetamide, and the enzymatic activity after alkylation is affected. And the nearby sequence Gln-Gly-Gln-Cys is conserved in human and horse acetaldehyde dehydrogenase, indicating that Cys-302 plays an important role in catalytic activity.

Site-directed mutagenesis of hepatic acetaldehyde dehydrogenase revealed that glutamate-268 is also a residue required for catalytic activity. The activity of the mutated enzyme could not be recovered by the addition of a common base, suggesting that this residue may be used to react with the initial activation of cysteine-302, rather than only the deacylation or hydrogen transfer step.

The acylated acetaldehyde dehydrogenase in bacteria forms a bifunctional dimer with the metal-dependent 4-hydroxy-2-ketovalerate aldolase. This complex is responsible for the metabolism of toxic aromatic compounds in bacteria. The combination of the two units creates a hydrophobic channel between the active centers, and the intermediate is transported to the other end upon completion of the reaction, improving catalytic efficiency and avoiding side reactions.

 

Nature

A zinc-containing enzyme. Its molecule consists of two subunits, one of which is located at the active center of the enzyme and the other acts to stabilize the quaternary structure. In the presence of coenzyme, I, it catalyzes the dehydrogenation of certain primary or secondary alcohols, aldehydes and ketones including ethanol, catalyzing the dehydrogenation of n-butyraldehyde, cinnamaldehyde and benzaldehyde over acetaldehyde. The desorbed hydrogen is accepted by NAD to make it a reduced coenzyme I. Serum alcohol dehydrogenase activity is a diagnostic value for acute hepatitis parenchymal cell damage. Serum enzyme activity was negative in normal or non-recurrent liver disease patients.

 

Classification

  1. Greenfield uses the horse ALTH isoenzyme to name it. The ALDH located in the cytosol is named ALDH1, and the ALDH located in the mitochondria is ALDH2.
  2. ALDH was later named ALDH1, ALDH2, ALDH3, and ALDI-Lt according to the sequence of ALDH forward electrophoretic migration reduction and isoelectric point increase.
  3. Mammal aldehyde dehydrogenase can be divided into three categories according to the location, structure and kinetics of its subcellular and the similarity of the original sequence:

The first type is cytoplasmic (ALDH1), the second type is mitochondria (ALDH2), and the third type is inducible cytoplasmic aldehyde dehydrogenase and inducible microsome acetaldehyde dehydrogenase (Such as ALDH3).

As of 2012, the first two types of acetaldehyde dehydrogenase have been extensively studied and found to be effective in promoting the oxidation of short-chain aliphatic aldehydes and aromatic aldehydes. In contrast, studies on the third type of aldehyde dehydrogenase are less common in the study of microsomal aldehyde dehydrogenase, and microsomes are found in rat liver, rabbit intestine, human liver, and human white blood cells. The presence of acetaldehyde dehydrogenase, but the mechanism of action is not clear.

 

Distribution

The acetaldehyde dehydrogenase gene is located on chromosome 12 (12q24.2), and its major polymorphism is rs671, which is G1510A located in exon 12. The normal allele is denoted as ALDH2*1, and the allele of the single base mutation is denoted as ALDH2*2. In the enzyme in which the mutant gene is translated, the glutamic acid of residue 487 becomes lysine, resulting in a substantial loss of catalytic activity.

The distribution of ALDH2*2 in different ethnic groups is different, and it basically appears in Asians. Whites ~0%, blacks ~0%.

 

Effect

The alcohol dehydrogenase in the liver is responsible for oxidizing ethanol (the component of the wine) to acetaldehyde, and the resulting acetaldehyde is further converted into a harmless acetic acid (i.e., a component of vinegar) by acetaldehyde dehydrogenase as a substrate. Acetaldehyde is more toxic than ethanol and is one of the main causes of hangovers. Moreover, acetaldehyde is suspected of being carcinogenic, and it has a certain relationship with the occurrence of human tumors. The main acetaldehyde conversion in the human body is acetaldehyde dehydrogenase (ALDH) in the liver. There is a significant difference in the catalytic rate between ALDH1 and ALDH2. The K_M of ALDH2 to acetaldehyde is lower than ALDH1, about 1/ of the latter. 10, is an isozyme mainly responsible for the conversion of acetaldehyde.

 

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