The idea in this group transfer reaction is to have the -OH group on the C6 alcohol carbon of glucose to "attack" the terminal phosphate of ATP.

-OH is not a good attacking agent for a group transfer reaction- it would be much better if it were unprotonated -O^- instead.

Both substrates (Glucose and ATP) must be in the active site at the same time.
The first step in the catalysis after both substrates have bound to the active site involves "base catalysis". An amino acid side chain (Asparate in the case of hexokinase) helps to remove a proton from the -OH to generate the required -O^- and the protonated Aspartic Acid.
The -O^- attacks the terminal phosphate.
This causes "too many bonds" to phosphate so one pair of electrons must exit - these end up as a minus charge on what used to be the "middle" phosphate of ATP.

The results are shown. The H from the -OH group on C6 is now on the amino acid side chain. The phosphate group has been transferred to the alcohol carbon of glucose and ADP is the other product.

Aerobic Glucose Metabolism

Complex III, Coenzyme Q Oxidase, Cytochrome bc₁

Reaction

Rationale

Thermodynamics

Mechanism

Pictures

JMOL

Enzyme Name	Complex III, Coenzyme Q Oxidase, Cytochrome bc₁ These are all synonyms

Reaction Catalyzed	REDOX
Reaction Type	Oxidation Reduction
Pathway Involvement	Oxidative Phosphorylation
Cofactors/Cosubstrates	cofactors heme Coenzyme Q (one permanently bound) iron sulfur clusters cosubstrates: Coenzyme Q and a small protein - cytochrome c.

ΔG^o'	-19.0 kJ/M (NOTE: This does not take any H⁺ gradient into account)	Starting from standard state (all concentrations at 1 M/l) and allowing the reaction to come to equilibrium the products (reduced cytochrome c and CoQ) concentration would end up ~1700 times higher than that of the substrates - (oxidized cytochrome c and CoQH²).
	The Standard Free Energy favors moving electrons in the direction of oxidative phosphrylation.
Comments	The ΔG°' for this reaction as stated above only takes the chemistry into account. This is actually not the case. Since the electron transfer is inextricably linked to H⁺ gradient generation, this too must be taken into account. The ΔG_total = The ΔG_ET + The ΔG_H⁺grad ΔG_ET= due to electron transfer. ΔG_H⁺grad= the ΔG due to the proton gradient
ΔG in a typical mitochondrion
	varies but is pretty close to 0

Mechanism for Chemistry
Complete Mechanism for Enzyme
	H⁺ pumping in complex III is an extremely complex series of events. The light blue rectangle represents the membrane. (The black H⁺ represents more while the red H⁺ represents fewer protons) CoQH₂ (reduced form) approaches complex III. Hemes and iron sulfur cluster are initially all oxidixed. 2 e^- are transferred to complex III. and the two H⁺ from CoQH₂ are released to the inter membrane space. This reduces both hemes (hemes can only take 1 electron each) One of those electrons is transferred to cytochrome c. The other to the on board CoQ. (hemes are now both oxidized and the CoQ is a 1 electron reduced radical which takes a H⁺ from the inner matrix as well) ANOTHER reduced CoQH₂ transfers its electrons to complex III and its 2H⁺ to the inter membrane space. (both hemes are again reduced) One electron is transferred to cytochrome c while the other is transferred to the on board CoQ (also taking up a H⁺ from the inner matrix and making the fully reduced CoQH₂). The on board CoQH₂ then transfers both electrons and both H⁺ to an EXTERNAL CoQ. The end result - 2 e^- transferred, 4 H⁺ released to the intermembrane space.


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Pictures of Enzyme with substrate

Aerobic Glucose Metabolism

Complex III, Coenzyme Q Oxidase, Cytochrome bc1

Complex III, Coenzyme Q Oxidase, Cytochrome bc1

Complex III, Coenzyme Q Oxidase, Cytochrome bc₁

Complex III, Coenzyme Q Oxidase, Cytochrome bc₁