Gerty Theresa Cori (1896-1957) was awarded a quarter of the 1947 Nobel Prize in Physiology or Medicine for her discovery of how glycogen is broken down and resynthesized in the body to be either used or stored as a source of energy. Her initial research was physiological in nature, and focused on the role of epinephrine in glycogen metabolism. This led to research of a more biochemical nature, including investigations on glycogen breakdown in minced frog muscle. In 1936, she isolated glucose-1-phosphate – also called the Cori ester -- and established that it was a breakdown product of glycogen. Cori also characterized glycogen phosphorylase, the enzyme responsible for breakdown of glycogen to glucose 1-phosphate. In the 1940s, Cori began to purify and crystallize some of the enzymes that she and her husband, Carl, had earlier described, such as glycogen phosphorylase. Cori also elucidated the molecular defects underlying a number of genetically determined glycogen storage diseases.