CITRIC ACID CYCLE -Pyruvate Dehydrogenase Reading: Harper’s Biochemistry Chapter 18 Lehninger Principles of Biochemistry 3rd Ed. pp. 567-583 OBJECTIVES
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Pyruvate + NAD+ + CoAAcetyl-CoA + NADH + H+ + CO2
1. pyruvate dehydrogenase (E1)
2. dihydrolipoyl transacetylase (E2)
3. dihydrolipoyl dehydrogenase (E3)
1. thiamine pyrophosphate (TPP)
2. flavin adenine dinucleotide (FAD)
3. coenzyme A (CoA)
4. nicotinamide adenine dinucleotide (NAD)
GTP + ADP GDP + ATP
The two carbons appearing as CO2 are not the same two carbons that entered the cycle as the acetyl group of acetyl-CoA (they are in oxaloacetate, and will be released in subsequent cycles)
The cycle generates the equivalent of 12 ATP’s from one acetyl-CoA (3 NADH = 9 ATPs, 1 FADH2 = 2 ATPs, 1 ATP (GTP) directly)
1. Riboflavin - in the form of flavin adenine dinucleotide (FAD), a cofactor in the dehydrogenase complexes.
2. Niacin - in the form of nicotinamide adenine dinucleotide (NAD), a cofactor for three dehydrogenases.
3. Thiamine/vitamin B - as thiamine dephosphate, the coenzyme for the -ketoglutarate dehydrogenase reaction.
4. Pantothenic acid - a part of coenzyme A, the cofactor attached in acetyl-CoA and succinyl-CoA