Summary
This paper, published by Gerty Cori in collaboration with Carl Cori, establishes that the enzyme phosphorylase is the primary catalyst for the first step of glycogenolysis—the cleavage of glycogen to glucose-1-phosphate. The central thesis is that phosphorylase, not a hypothetical "diastase" or other nonspecific enzyme, specifically and reversibly breaks the α-1,4-glycosidic bonds in glycogen, initiating its breakdown in animal tissues. The Coris demonstrate this through precise biochemical assays using purified liver and muscle extracts, showing that the reaction requires inorganic phosphate and yields a phosphorylated sugar. A key finding is that phosphorylase activity is regulated by hormonal and metabolic signals, such as epinephrine and glucose levels, linking glycogen breakdown to systemic energy demands. The reader takes away a mechanistic understanding of how stored glycogen is mobilized into a metabolically usable form, laying the foundation for later work on enzyme regulation and signal transduction.
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Key concepts
- Glycogenolysis — The enzymatic breakdown of glycogen into glucose-1-phosphate, catalyzed by phosphorylase, to provide rapid glucose for energy.
- Phosphorylase — The enzyme that cleaves α-1,4-glycosidic bonds in glycogen using inorganic phosphate, producing glucose-1-phosphate without ATP hydrolysis.
- Glucose-1-phosphate — The phosphorylated intermediate formed from glycogen breakdown, which is then converted to glucose-6-phosphate for glycolysis or glucose release.
- Inorganic phosphate (Pi) — The required co-substrate for phosphorylase, incorporated into the sugar molecule during cleavage.
- Hormonal regulation of phosphorylase — The activation of phosphorylase by epinephrine and glucagon via cyclic AMP cascades, linking glycogenolysis to stress or low blood glucose.
- Cori cycle — The metabolic pathway in which lactate from muscle glycogenolysis is converted back to glucose in the liver, though this concept was more fully developed later.