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 activeb) 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. Low O2 levels, PDK active- when PDK is active PDH is inactive, oxidative metabolism is limited

High O2 levels, active PDH- oxidative metabolism is increased

High O2 levels, PDK inhibitor present- PDH is active, oxidative metabolism is increased

High O2 levels, inactive PDH- oxidative metabolism is limited

High O2 levels, PDPK active- , oxidative metabolism is increased

PDH is regulated via phosphorylation by PDK: when PDK phosphorylates PDH, it becomes inactive. The opposite of that PDK activated PDH by dephosphorilation of PDH.

2. The correct answer is: It is processed to lactate.

This would occur under the anaerobic conditions (absence of oxygen) in a process called fermentation. After the production of pyruvate in glycolysis, the next step is anaerobic conversion of pyruvate to lactate by the enzyme lactate dehydrogenase.

This is a process the only way of glucose utilization and ATP production in erythrocytes (no mitochondria) and in exercising muscle cells (lack of oxygen).