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Classification and function of mitochondrial respiratory chain complex

Date:2022-09-02 Views:307

The respiratory chain is a continuous reaction system composed of a series of hydrogen donors and electron donors arranged in a certain order. It transfers the paired hydrogen atoms removed from metabolites to oxygen to produce water, and at the same time ATP is produced. In fact, the role of the respiratory chain represents the most basic function of mitochondria. The hydrogen and electron donors in the respiratory chain are carriers that can transmit hydrogen atoms or electrons. Since hydrogen atoms can be regarded as composed of H+ and e, Hydrogen donors are also electron donors. The essence of hydrogen donors and electron donors are enzymes, coenzymes, prosthetic groups or cofactors. All the prosthetic groups for electron transfer in the mitochondrial respiratory chain include: NADH, FAD, FMN, iron-sulfur center, ubiquinone, copper center and cytochrome α, α3, bH, bL, c, c1. The corresponding enzymes and prosthetic groups do not work alone, but combine with each other to form a relatively independent function of the respiratory chain protein complex, namely respiratory chain complex I, respiratory chain complex II, respiratory chain complex III, respiratory chain complex IV, respiratory chain complex IV, and respiratory chain complex V.


1.Respiratory chain complex Ⅰ

Most of the ATP in mitochondria is complex I. Respiratory chain complex I is the most complicated complex monomer, composed of 45 protein subunits, 8 iron-sulfur centers and 1 FMN molecule, and can bind NADH, NADPH and coenzyme Q. Respiratory chain complex I is composed of a transmembrane arm and a hydrophilic arm extending into the mitochondrial matrix. The connection between the hydrophilic arm and the transmembrane arm is L-shaped. The hydrophilic arm completes the oxidation of NADH and transfers electrons to the area where the two arms connect; the transmembrane arm completes the reduction of coenzyme Q and the transport of protons. The coordination of functions between the two arms is completed by the interaction and conformational changes of a series of protein subunits.

2.Respiratory chain complex Ⅱ

Complex II is composed of succinate dehydrogenase and an iron-sulfur protein, which transfers electrons obtained from succinate to coenzyme Q. Cytochromes are all red or brown with heme as the auxiliary group. Transfer electrons from coenzyme Q to oxygen. Respiratory chain complex II obtains electrons from FADH and transfers the electrons to oxidized ubiquinone Q to generate reduced ubiquinone QH2. There is no transmembrane transport of protons during the whole process. The protein structure of respiratory chain complex II is relatively simple, consisting of 4 protein subunits. Respiratory chain complex II and respiratory chain complex I, respiratory chain complex III, and respiratory chain complex IV have different functions. They do not transport protons and can be regarded as a bypass of the electron transport chain. Many protein complexes with similar functions to respiratory chain complex II have been discovered, such as flavoprotein coenzyme Q oxidoreductase, dihydroorotate dehydrogenase, choline dehydrogenase, etc. They accept different electron donors The electrons eventually pass the electrons to coenzyme Q, but do not mediate the transport of protons. This shows that the mitochondrial electron transport chain is composed of the main chain composed of respiratory chain complex I, respiratory chain complex III, and respiratory chain complex IV and many branch chains to accept electron donors from different metabolic pathways and ultimately reduce oxygen. Generate water.

3.Respiratory chain complex Ⅲ

Respiratory chain complex III polymerizes itself to form a dimer, and each monomer contains 11 protein subunits, an iron-sulfur center, and a variety of cytochromes. Respiratory chain complex III obtains electrons from reduced ubiquinone QH2 and transfers the electrons to cytochrome c, while using the released energy to pump protons into the membrane gap. Based on its structural information, scientists have proposed a variety of models of the mechanism of action of respiratory chain complex III, and the most influential one is the Q-Cycle model.

4.Respiratory chain complex Ⅳ

Respiratory chain complex IV: Cytochrome C oxidase complex. Transfer electrons to oxygen. Respiratory chain complex IV contains 14 protein subunits and various prosthetic groups, which catalyze the last step of electron transfer. To put it simply, the electrons from cytochrome c in CIV are transferred to cytochrome α through CuA, and then to the oxygen reaction center composed of cytochrome α3 and CuB. The energy released during the electron transfer process causes the conformation of CIV protein to change, which causes mitochondria A part of the protons in the matrix are transferred to the oxygen reaction center through the K channel and the D channel to reduce oxygen to produce water, while the other part of the proton is directly pumped into the mitochondrial membrane space through the H channel.

5.Respiratory chain complex V

Respiratory chain complex V is oxidative phosphorylation that is coupled with the four complex enzyme complexes of the respiratory chain to generate ATP, so it often becomes ATP synthase. Respiratory chain complex V is a rotatable enzyme that synthesizes ATP by forming a proton electrochemical potential gradient on both sides of the inner mitochondrial membrane during electron transport.

Abbkine meticulously developed research tools related to the electron transport chain: CheKine™ Micro Mitochondrial complex I-V Activity Assay Kit, which provides a more detailed and accurate detection method for complex I-V activity, compatible with detection Many types of samples.

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