Which of the following are respiratory enzymes?
- acetyl coenzyme A
- FAD
- reduced NAD
A. 1 and 2 only
B. 2 and 3 only
C. 1, 2 and 3
D. none of them
E. 1 and 3 only
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The correct answer is D.
Acetyl CoA
Acetyl coenzyme A is, like the name suggests, a coenzyme. It plays a key role in the metabolism of proteins, lipids and carbohydrates.
One of its purposes is to be a reaction intermediate to ultimately enable the production of ATP through the Krebs cycle (or citrate cycle).
It is NOT a respiratory enzyme.
FAD
FAD, or flavin adenine dinucleotide, helps catalyze redox reactions. It plays a key role in the processes of DNA repair, photosynthesis, and has an antioxidant role (removal of toxic free radicals).
More specific uses for FAD are its role as cofactor :
- for cytochrome B5 reductase, which helps maintain hemoglobin in its reduced state (which is its functional state)
- for glutathione reductase, which helps prevent red blood cells from oxidative stress.
It is NOT a respiratory enzyme.
Reduced NAD
Reduced NAD or NADH, is an electron and hydrogen donor. It is obtained by the processes of glycolysis and/or the Krebs cycle.
It helps with oxidative reactions such as the ones in the electron transport chain that ultimately produces ATP (by oxidative phosphorylation).
It is NOT a respiratory enzyme.
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