Question

Pyruvate dehydrogenase is the entry point for the glycolytic product pyruvate into oxidative metabolism (the citric acid cycle and oxidative phosphorylation). Because it occupies such an important checkpoint in metabolism, it is tightly regulated.

a) Determine whether the following conditions promote entry into oxidative metabolism or limit entry into oxidative metabolism. The following abbreviations may be used: PDH is pyruvate dehydrogenase; PDK is pyruvate dehydrogenase kinase; PDP is pyruvate dehydrogenase phosphatase.
Low O2 levels, PDK active;
High O2 levels, active PDH;
High O2 levels, PDK inhibitor present;
High O2 levels, inactive PDH;
High O2 levels, PDK active;
b) What is the fate of pyruvate (in a human) if a person has a phosphatase deficiency?
It is processed to lactate.
It is processed to acetyl-CoA.
It is processed to ethanol.

Answer 1

1. Answers;

• Low O2 levels, PDK active; - Limit
• High O2 levels, active PDH; - Promote
• High O2 levels, PDK inhibitor present; - Promote
• High O2 levels, inactive PDH; - Limit
• High O2 levels, PDK active; - Limit

PDH catalyze pyruvate to acetyl-CoA that enters the citric cycle. PDK negatively regulates PDH by phosphorylating one subunit hence suppressing catalytic activity of the enzyme.

2. The answer is; It is processed to lactate.

Phosphatase is an enzyme critical in the dephosphorylation of proteins in the body. Therefore, it acts in the positive regulation of PDH (by dephosphorylating the PDH subunit) after PDK inactivates PDH. Therefore, a subject with phosphatase deficiency will have his pyruvates turned to lactate because once PDK phosphorylates PDH, they remain inactive. Therefore the pyruvates cannot be catalyzed into acetyl-CoA