Summary

This book presents Gerty Cori's pioneering research on the enzymatic steps of glycogen breakdown and synthesis, establishing the Cori cycle as a fundamental metabolic pathway. The central thesis is that glycogen metabolism is regulated by specific enzymes—particularly glycogen phosphorylase and glucose-6-phosphatase—whose activities control blood glucose levels and energy storage in animal tissues. Cori details her experimental methods for isolating and characterizing these enzymes from liver and muscle, demonstrating how they interconvert glycogen and glucose. A reader gains a clear, mechanistic understanding of how the body mobilizes stored glycogen during exercise or fasting, and how defects in these enzymes cause metabolic diseases like von Gierke disease.

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Key concepts

Cori cycle — The metabolic pathway in which lactate produced by anaerobic glycolysis in muscle is converted back to glucose in the liver, then returned to muscle for energy.
Glycogen phosphorylase — The enzyme that catalyzes the rate-limiting step of glycogenolysis, cleaving glucose-1-phosphate from glycogen.
Glucose-6-phosphatase — The enzyme that dephosphorylates glucose-6-phosphate to free glucose, enabling its release into the bloodstream from the liver.
Von Gierke disease — A glycogen storage disease caused by deficiency of glucose-6-phosphatase, leading to severe hypoglycemia and glycogen accumulation in the liver.
Active vs. inactive phosphorylase — The discovery that glycogen phosphorylase exists in two interconvertible forms (phosphorylated active and dephosphorylated inactive), revealing hormonal regulation via phosphorylation.