Pyruvate dehydrogenase activity during aerobic respiration requires:-

Link reaction: If sufficient oxygen is available, each 3-carbon pyruvate molecule enters the mitochondrial matrix where its oxidation is completed by aerobic means. It is called a gateway step or link reaction between glycolysis and Krebs' cycle. Acetyl CoA is a common intermediate of fat and carbohydrate metabolism. Later, this acetyl CoA from both sources enters the TCA cycle. Link reaction also called oxidative decarboxylation reaction is not a part of Krebs' cycle.

$\mathrm{Pyruvate} + \mathrm{CoA} + {\mathrm{NAD}}^{+} \underset{{\mathrm{Mg}}^{+2}, \mathrm{TPP}, \mathrm{Lipoic} \mathrm{acid}}{\overset{\mathrm{Pyruvate} \mathrm{dehydrogenase}}{\to }} \mathrm{Acetyl} \mathrm{CoA} + \mathrm{NADH}.{\mathrm{H}}^{+} + {\mathrm{CO}}_2$