Dehydrogenases and Oxidoreductases

Dehydrogenase
Classification:
- Polyol dehydrogenases
- General classification
Cofactors:
- NAD⁺/NADH
- NADP⁺/NADPH
Classical members:
- Lactate dehydrogenase
- Alcohol dehydrogenase
- Glucose 6 phosphate dehydrogenase
- Pyruvate dehydrogenase
- Aldehyde dehydrogenase
- Succinate dehydrogenase
- Malate dehydrogenase
- Glutamate dehydrogenase
- Isocitrate dehydrogenase
- Glu/Leu/Phe/Val dehydrogenase

Oxidoreductase and Dehydrogenase definition

Generally, the enzymes that transfer electron from one molecule to another are called Oxidoreductase. These enzymes catalyze the oxidation reaction A+B^- ->A^-+B. In reality, free electrons do not exists as these reactions involve atoms transfer. Because most of metabolic oxidation reactions involve removing hydrogen from the electron donor, these enzymes are called dehydrogenases. The term oxidase is used only for the enzymes in which the oxidation reaction with molecular oxygen (O₂) participating as the electron acceptor.

Oxidases will not be concidered here. For more details please visit EC 1. Oxidoreductases page.

Dehydrogenase nomenclature

The common scheme for making names for oxidoreductases is adding donor name to the dehydrogenase, i.e. donor dehydrogenase. For example: alcohol dehydrogenase, leucine dehydrogenase etc. The proper name consists from the donor name, acceptor name together with oxidoreductase, i.e. donor:acceptor oxidoreductase. Sometimes the construction acceptor reductase is used.
Example: Enzyme EC 1.1.1.1
Systematic name: alcohol:NAD⁺ oxidoreductase
Accepted name: alcohol dehydrogenase

Enzymatic classification of dehydrogenases

According to the Enzyme Nomenclature from Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB) the nomenclature and classification of enzymes is based on the reaction they catalyse. Each reaction, catalysed by enzyme is specified by the Enzyme Commission number or EC number. Each EC number consists of the EC and for digits separated by periods. Each digit represents the progressively higher level of enzyme classification.

According to this classification, dehydrogenases are belongs to the EC 1 Oxidoreductases group.

Oxidoreductases classification according to the substrate they utilise:

EC 1.1 - Acting on the CH-OH group of donors
EC 1.2 - Acting on the aldehyde or oxo group of donors
EC 1.3 - Acting on the CH-CH group of donors
EC 1.4 - Acting on the CH-NH₂ group of donors
EC 1.5 - Acting on the CH-NH group of donors
EC 1.6 - Acting on NADH or NADPH
EC 1.7 - Acting on other nitrogenous compounds as donors
EC 1.8 - Acting on a sulfur group of donors
EC 1.9 - Acting on a heme group of donors
EC 1.10 - Acting on diphenols and related substances as donors
EC 1.11 - Acting on a peroxide as acceptor
EC 1.12 - Acting on hydrogen as donor
EC 1.13 - Acting on single donors with incorporation of molecular oxygen (oxygenases)
EC 1.14 - Acting on paired donors, with incorporation or reduction of molecular oxygen
EC 1.15 - Acting on superoxide as acceptor
EC 1.16 - Oxidizing metal ions
EC 1.17 - Acting on CH or CH₂ groups
EC 1.18 - Acting on iron-sulfur proteins as donors
EC 1.19 - Acting on reduced flavodoxin as donor
EC 1.20 - Acting on phosphorus or arsenic in donors
EC 1.21 - Acting on X-H and Y-H to form an X-Y bond
EC 1.97 - Other oxidoreductases
EC 1.98 - Enzymes using H₂ as reductant
EC 1.99 - Other enzymes using O₂ as oxidant

Structural classification of dehydrogenases

Currently, two different classifications of dehydrogenases are exists. One is historical for polyol dehydrogenases and another is modern UniProt protein classification for dehydrogenases and oxydoreductases. Generally we recommend using UniProt classification, but for polyol dehydrogenases you still can use ancient classification, but it is necessary to remember, that these classification are slightly different. Please also remember, that alcohol dehydrogenase classification is slightly inconsistent.

Dehydrogenase catalytic mechanism

Dehydrogenases transfer protons to an acceptor or coenzymes, i.e. small organic molecules, involved into enzymatic catalysis, such as Nicotinamide adenine dinucleotide (NAD⁺ or NADH), Nicotinamide adenine dinucleotide phosphate (NADP⁺ or NADPH), Flavin adenine dinucleotide (FAD) or Flavin mononucleotide (FMN).

The wide diversity of dehydrogenases does not allow to develop a uniform catalytic mechanism for all cases. For each new dehydrogenase structure this mechanism should be scrutinized. Here, some common mechanisms are shown. For further reading about these mechanisms please refer to the original papers listed in the reference section.