What does succinyl-CoA do in the citric acid cycle?
Succinyl-CoA synthetase (SCS) is the only mitochondrial enzyme capable of ATP production via substrate level phosphorylation in the absence of oxygen, but it also plays a key role in the citric acid cycle, ketone metabolism and heme synthesis.
Is succinyl-CoA part of the citric acid cycle?
The citric acid cycle intermediate succinyl-CoA plays an important role in fatty acid and amino acid metabolism because it is the entry point of odd-chain fatty acids, propionate, and the branched chain amino acids valine and isoleucine into the citric acid cycle.
How is valine converted to succinyl-CoA?
After transamination and decarboxylation of valine, a series of oxidation reactions converts the remaining four carbons into methylmalonyl-CoA, which is transformed into succinyl-CoA. Some parts of the valine and isoleucine degradative pathways closely parallel steps in fatty acid degradation (Chapter 16).
Why is succinyl-CoA an appropriate signal for regulation of the citric acid cycle?
Succinyl-CoA is an intermediate of the citric acid cycle—the first four-carbon intermediate, formed in the a-ketoglutarate dehydrogenase reaction. Its accumulation signals reduced flux through the cycle, and thus the need for reduced entry of acetyl-CoA into the cycle.
What does succinyl-CoA inhibit?
In vitro, it inhibits histidine phosphorylation of mitochondrial succinyl CoA synthetase.
Which product of the citric acid cycle is created when succinyl-CoA is converted into succinate?
Succinate thiokinase converts succinyl-CoA to succinate, while first generating ATP/GTP by substrate-level phosphorylation. Succinate is acted upon by succinate dehydrogenase, requiring FAD and Fe-S proteins to form fumarate.
What kind of reaction is succinyl-CoA to succinate?
Succinyl coenzyme A synthetase (SCS, also known as succinyl-CoA synthetase or succinate thiokinase or succinate-CoA ligase) is an enzyme that catalyzes the reversible reaction of succinyl-CoA to succinate….Succinyl coenzyme A synthetase.
|Succinate—CoA ligase (ADP-forming)|
How is valine synthesized?
Valine, like other branched-chain amino acids, is synthesized by plants, but not by animals. It is synthesized in plants and bacteria via several steps starting from pyruvic acid. The initial part of the pathway also leads to leucine. The intermediate α-ketoisovalerate undergoes reductive amination with glutamate.
How does NADH regulate the citric acid cycle?
It regulates the speed at which the citrate isomer isocitrate loses a carbon to form the five-carbon molecule α-ketoglutarate. The coenzyme NADH is a product of the reaction and, at high levels, acts as an inhibitor by directly displacing the NAD+ molecules it is formed from.
Why does succinyl-CoA inhibit citrate synthase?
Thus, succinyl-coA serves as a competitive feedback inhibitor of citrate synthase by inhibiting over catalysis of the citric acid cycle and stopping further catabolism (8). Finally, citrase itself regulates the activity of citrate synthase by competing with oxaloacetate for the binding to the active site.
What high energy molecule is produced during the hydrolysis reaction of succinyl-CoA to succinate?
GTP, produced by the conversion of succinyl-CoA to succinate, is a direct source of high-energy compounds.
What is reaction involved in Succinyl CoA to succinate?
Succinyl CoA synthetase catalyzes the following reversible reaction: Succinyl CoA + Pi + NDP ↔ Succinate + CoA + NTP. The enzyme then utilizes a histidine residue to remove the phosphate group from succinyl phosphate and generate succinate.