Succinyl-CoA Synthetase

Enzyme Name	Succinyl-CoA Synthetase

Reaction Catalyzed	two step reaction: Group Transfer Group Transfer
Reaction Type	Two Step Reaction Group transfer Group Transfer
Pathway Involvement	Citric Acid Cycle
Cofactors/Cosubstrates	The ADP "equivalent" GDP and PO₄⁼ (phosphate) are co-substrates and the ATP "equivalent" GTP and coenzyme A are co-products. no other cofactors are required

Rationale

The goal here is to stick a phosphate onto the end of GDP (add a phosphate to another phospate)

BUT We already know that one cannot just stick a phosphate onto another phosphate group without some other intervention because this would just be a reverse hydrolysis which are extremely dififcult to reverse in water.

The "bare" phospate with then be transferred a couple times initially taking advantage of the thioester of succinyl-CoA

the phosphate intially attacks the thioester so the leaving group is not water but Coenzyme A - this makes a group transfer reaction.

THEN the resulting phosphoanhydride (phosphate on an organic acid) = through another intermediate step as well - CAN transfer the phosphate to the end of GDP

ΔG^o'	-3.0 kJ/M
	The Standard Free Energy favors moving the citric acid cycle in the "correct" direction. (but not by much)
K_eq		Since this fraction is greater than 1, then the concentrations of the substances on top (succinate GTP and CoA) must be larger than those on the bottom WHEN the reaction comes to equilibrium.
Comments	Starting from standard state (all concentrations at 1 M/l) and allowing the reaction to come to equilibrium the products succinate and GTP concentration would end up ~15 times higher than that of the substrate - succinyl-CoA and GDP + PO₄⁼.
ΔG in a typical mitochondrion
	~0 kJ/M	This reaction is readily reversible expecially at physiological conditions where the concentrations of substrates and products are at levels that ensure that the observed forward and reverse rates are about equal

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Aerobic Glucose Metabolism

Succinyl-CoA Synthetase Information

Succinyl-CoA Synthetase