Phosphorylase and Related Enzymes of Glycogen Metabolism

The finding that pyridoxal phosphate is an essential constituent or coenzyme of glycogen phosphorylase created a new dimension for thought concerning the functions of vitamin B6. This chapter explores questions, such as “Did the discovery of vitamin B6 in phosphorylase stimulate avenues of approach that have led to new disclosures concerning functions of vitamin B6? Have any of the classical findings of vitamin B6 deficiency been explained as a consequence of impaired phosphorylase activity?” The chapter reviews the progress that has been made in several laboratories as to the mechanism of action of pyridoxal phosphate in phosphorylase. In view of the complex role of phosphorylase in the regulation of glycogen metabolism, the chapter focuses on the phosphorylase system. The interconversion reactions of the two forms of phosphorylase catalyzed by phosphorylase b kinase and phosphorylase phosphatase are briefly reviewed. The chapter evaluates the role of vitamin B6 in carbohydrate metabolism in general.