Glycogen phosphorylase in Dictyostelium discoideum. II. Synthesis and degradation during differentiation.

A purified preparation of glycogen phosphorylase from Dictyostelium discoideum was used to elicit specific antisera in rabbits. The antisera were used to quantitate the amount of precipitable phosphorylase protein from cell extracts prepared at various stages of the developmental cycle. Following isotope incorporation studies in differentiating cells, the specific radioactivity of enzyme isolated by antibody precipitation was compared to that of acid-insoluble protein. Prior to 5 hours of development, glycogen phosphorylase could not be detected enzymatically or immunologically. Between aggregation and culmination, the rate of enzyme synthesis increased about 6-fold, then decreased to an insignificant value in young sorocarps. The rate of enzyme degradation was negligible during the period of maximal enzyme accumulation, then increased to a peak value of 40% after culmination, coincident with a rapid drop in phosphorylase activity. The data indicated that the increase in glycogen phosphorylase activity during development results from an increase in the rate of enzyme synthesis.