CITRIC ACID CYCLE -Pyruvate Dehydrogenase Reading: Harper’s Biochemistry Chapter 18 Lehninger Principles of Biochemistry 3rd Ed. pp. 567-583 OBJECTIVES
Sources of acetyl-CoA in mitochondria steps of cellular respiration
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
Products of one turn of the citric acid cycle. Three NADH, one FADH2, one GTP (or ATP), and two CO2 are released in oxidative decarboxylation reactions. All cycle reactions are shown in one direction only, but keep in mind that most of the reactions are reversible.
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