Question

In muscle cells under physiological conditions, the measured ratio of [Pi]/[glucose 1-phosphate] is more than 100:1. What does this indicate about the direction of the metabolite flow through the glycogen phosphorylase reaction in muscle?

Answer 1

A high ratio of [Pi]/[glucose 1-phosphate] in muscle cells indicates that metabolite flow is directed towards glycogen breakdown to glucose 1-phosphate, facilitated by glycogen phosphorylase, to produce ATP in response to energy demands.

Step-by-step explanation:

If the ratio of inorganic phosphate (Pi) to glucose 1-phosphate ([Pi]/[glucose 1-phosphate]) is more than 100:1 in muscle cells under physiological conditions, this indicates that the flow of metabolites through the glycogen phosphorylase reaction is towards glycogen breakdown rather than synthesis.

This is because a high ratio implies that there is a high concentration of Pi available, which favors the reaction catalyzed by glycogen phosphorylase to produce glucose 1-phosphate from glycogen. In muscle cells, adrenaline (epinephrine) stimulates the breakdown of glycogen to glucose 1-phosphate via the activation of glycogen phosphorylase.

This process ensures a ready supply of glucose for ATP production, especially during periods of increased energy demand, such as during exercise or in response to stress in the 'fight or flight' reflex. Thus, the high [Pi]/[glucose 1-phosphate] ratio supports the physiological role of muscle glycogen as a quick source of glucose to produce ATP during times when immediate energy is required.