Question

In many tissues, one of the earliest responses to cellular injury is a rapid increase in the level of enzymes involved in the pentose phosphate pathway. Ten days after an injury, heart tissue has levels of G6PD and 6-phosphogluconate dehydrogenase that are 20 to 30 times higher than normal, whereas the levels of glycolytic enzymes are only 10 to 20% of normal. Suggest an explanation for this phenomenon.

Answer 1

Pentose phosphate pathway

Explanation:

• Ten days after an injury, there is still cellular and tissue repair going on. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase are two enzymes involved in the pentose phosphate pathway which are also found in abundance in neutrophils and macrophages. These phagocytic cells of the immune system utilize NADPH to generate superoxide radicals from molecular oxygen, which are used to kill the pathogens or damaged cells they have ingested. The great rise in these two enzymes could be coming from these immune cells as they are cleaning up the damaged tissue.
• Additionally, these immune cells use these two enzymes to produce NADPH, which can be used to counterbalance oxidative stress via the action of the glutathione system. Injured tissue can cause oxidative stress and increase the need for action from the glutathione system.
• The glycolytic enzyme activity would be decreased as some of the glucose is shunted to the pentose phosphate pathway to favor tissue repair over the ATP generation which comes from the glycolytic pathway reactions.