This project continues and extends work carried out on the relationship between structure and function of glycogen phosphorylase. The amino acid sequence of the enzyme is being determined; approximately 30% of its structure has been resolved, including the structure of two of its functional sites. A second aspect of this project relates to the regulation of glycogen breakdown in which phosphorylase is involved. While much is known about the reactions that trigger this metabolic process, the way in which the activated enzymes are returned to their inactive (resting) state is still obscure. The properties of one such enzyme, phosphorylase phosphatase, are being investigated. A third purpose of this research is to attempt to define how regulatory mechanisms arose in early species and evolved with time. Work has been initiated on the control of carbohydrate metabolism in the Pacific dogfish which has separated from the main line of evolution leading to mammals 450 million years ago, and on yeast which is of intermediate complexity between bacteria and higher fungi.