Excess glucose is stored as glycogen inside the body. The Coris showed that glycogen phosphorylase removes glucose units as glucose-1-phosphate using inorganic phosphate, an energy-saving phosphorolysis reaction. The product is converted to glucose-6-phosphate by phosphoglucomutase and enters glycolysis. These findings, later called the “Cori cycle,” explained how muscles and liver exchange lactate and glucose during exercise. Their discovery greatly advanced diagnosis and treatment strategies for diabetes and glycogen storage diseases.

In the 1930s the intermediate liberated from glycogen was unknown. The Coris added inorganic phosphate to muscle extracts and identified large amounts of glucose-1-phosphate—the Cori ester—via chromatography. They demonstrated that phosphorylase is reversible and requires pyridoxal-5′-phosphate as a prosthetic group. They then purified phosphoglucomutase and established reaction kinetics. The work launched quantitative enzymology and became a prototype for modern flux analysis. They also revealed AMP- and Ca2+-mediated control that supports rapid muscle contraction, influencing sports science and drug discovery.

The Coris quantified AMP-dependent activation and ATP/Glc-6-P feedback of phosphorylase a/b. They conceptualized phosphorolysis, proposing an ATP-independent yet efficient glycogenolysis model. Using 32P tracing combined with diffusion modeling, they calculated intracellular fluxes and suggested a ping-pong mechanism for phosphoglucomutase. They mathematically related phosphorylase Vmax and glycogen synthase Km to steady-state glycogen pools. Their methodology foreshadowed modern stable-isotope metabolomics.