8.4:
Pyruvate Oxidation
In the presence of oxygen, the charged pyruvate molecules — the final product of glycolysis, must enter the eukaryotic mitochondria to undergo pyruvate oxidation.
Since the enzymes for the reaction are present in the mitochondrial matrix, pyruvate needs to cross the mitochondrial double membrane.
Thus, it uses the porins present on the outer mitochondrial membrane and the mitochondrial pyruvate carrier on the inner membrane to reach the mitochondrial matrix.
Inside the matrix, it binds to the pyruvate dehydrogenase complex, composed of multiple copies of 3 types of enzymes.
In the first step of the reaction, the carboxyl group is removed from pyruvate and released as carbon dioxide.
The two-carbon molecule is oxidized to an acetyl group, and the released electrons reduce NAD+ into NADH and H+.
Finally, the acetyl group is transferred to coenzyme A, resulting in the formation of acetyl coenzyme A, which then enters the citric acid cycle to be further oxidized.
8.4:
Pyruvate Oxidation
After glycolysis, the charged pyruvate molecules enter the mitochondria via active transport and undergo three enzymatic reactions. These reactions ensure that pyruvate can enter the next metabolic pathway so that energy stored in the pyruvate molecules can be harnessed by the cells.
First, the enzyme pyruvate dehydrogenase removes the carboxyl group from pyruvate and releases it as carbon dioxide. The stripped molecule is then oxidized and releases electrons, which are then picked up by NAD+ to produce NADH, forming acetate.
Finally, coenzyme A—a sulfur-containing compound derived from a B vitamin—attaches to the acetate via its sulfur atom to create acetyl coenzyme A, or acetyl CoA. Acetyl CoA then moves into the citric acid cycle where it will be further oxidized.
Suggested Reading
Schell, John C, and Jared Rutter. “The Long and Winding Road to the Mitochondrial Pyruvate Carrier.” Cancer & Metabolism 1 (January 23, 2013): 6. [Source]
McCommis, Kyle S., and Brian N. Finck. “Mitochondrial Pyruvate Transport: A Historical Perspective and Future Research Directions.” The Biochemical Journal 466, no. 3 (March 15, 2015): 443–54. [Source]