5.5B: Oxidoreductase Protein Complexes
- Recognize the function of oxidoreductase protein complexes
In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another the oxidant, also called the electron acceptor. This group of enzymes usually utilizes NADP or NAD+ as cofactors.
For example, an enzyme that catalyzed this reaction would be an oxidoreductase: A– + B → A + B–. In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor).
In biochemical reactions, the redox reactions are sometimes more difficult to see, such as this reaction from glycolysis: Pi + glyceraldehyde-3-phosphate + NAD+ → NADH + H+ + 1,3-bisphosphoglycerate. In this reaction, NAD+ is the oxidant (electron acceptor) and glyceraldehyde-3-phosphate is the reductant (electron donor).
Oxidoreductases are classified as EC 1 in the EC number classification of enzymes. Oxidoreductases can be further classified into 22 subclasses:
- EC 1.1 includes oxidoreductases that act on the CH-OH group of donors (alcohol oxidoreductases);
- EC 1.2 includes oxidoreductases that act on the aldehyde or oxo group of donors;
- EC 1.3 includes oxidoreductases that act on the CH-CH group of donors (CH-CH oxidoreductases);
- EC 1.4 includes oxidoreductases that act on the CH-NH 2 group of donors (Amino acid oxidoreductases, Monoamine oxidase);
- EC 1.5 includes oxidoreductases that act on CH-NH group of donors;
- EC 1.6 includes oxidoreductases that act on NADH or NADPH;
- EC 1.7 includes oxidoreductases that act on other nitrogenous compounds as donors;
- EC 1.8 includes oxidoreductases that act on a sulfur group of donors;
- EC 1.9 includes oxidoreductases that act on a heme group of donors;
- EC 1.10 includes oxidoreductases that act on diphenols and related substances as donors;
- EC 1.11 includes oxidoreductases that act on peroxide as an acceptor (peroxidases);
- EC 1.12 includes oxidoreductases that act on hydrogen as donors;
- EC 1.13 includes oxidoreductases that act on single donors with incorporation of molecular oxygen (oxygenases);
- EC 1.14 includes oxidoreductases that act on paired donors with incorporation of molecular oxygen;
- EC 1.15 includes oxidoreductases that act on superoxide radicals as acceptors;
- EC 1.16 includes oxidoreductases that oxidize metal ions; EC 1.17 includes oxidoreductases that act on CH or CH2 groups;
- EC 1.18 includes oxidoreductases that act on iron-sulfur proteins as donors;
- EC 1.19 includes oxidoreductases that act on reduced flavodoxin as a donor;
- EC 1.20 includes oxidoreductases that act on phosphorus or arsenic in donors;
- EC 1.21 includes oxidoreductases that act on X-H and Y-H to form an X-Y bond; and EC 1.97 includes other oxidoreductases.
Key Points
- The reductant is the electron donor.
- The oxidant is the electron acceptor.
- This group of enzymes usually utilizes NADP or NAD+ as cofactors.
Key Terms
- oxidoreductase : Any enzyme that catalyzes an oxidation-reduction (redox) reaction.
- enzyme : A globular protein that catalyses a biological chemical reaction.
- catalyzes : Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself.