MEDizzy - If the turnover number of all enzymes involved in glycogen

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Glycogen Metabolism

If the turnover number of all enzymes involved in glycogen metabolic regulation and activity is 100 reactions per second, how many glucose molecules could be removed from glycogen in 1 s upon activation of one molecule of protein kinase A (PKA)?

ExplanationOne active PKA can activate in 1 s 100 molecules of phosphorylase kinase. Each phosphorylase kinase can, in 1 s activate 100 molecules of glycogen phosphorylase (so at this point we have 100 times 100 active molecules of phosphorylase, or 10,000 active phosphorylase molecules). Each active phosphorylase molecule can release 100 glucose residues per second from glycogen, and since there are 10,000 active phosphorylase molecules, 1,000,000 molecules of glucose are released per second once a single molecule of PKA has been activated. This is an example of cascade amplification, in which an increase in the activity of just one molecule at the top of the cascade can result in a large response further down the cascade.