SEASONAL-VARIATIONS OF ACTIVITIES OF GLYCOGEN-DEGRADING ENZYMES IN ASCIDIAN MUSCLE

The activities of alpha-amylase, alpha-glucosidase, hexokinase (HK), phosphoglucomutase (PGM), and phosphorylase were determined monthly in fresh ascidian muscle and changes of glycolytic compounds during storage at 2-degrees-C were investigated bimonthly. Most of the enzymatic activities were lowest in summer and highest in winter. Alpha-glucosidase, HK, and PGM showed conspicuous changes seasonally while alpha-amylase and phosphorylase showed slight ones. Glycogen in fresh ascidian muscle was highest in summer and lowest in winter wherease glucose showed a seasonal change in the opposite manner. Glucose 6-phosphate, fructose 6-phosphate, and lactic acid in fresh muscle fluctuated throughout the year and their seasonal variations were obscure. During storage, glycogen was degraded and other metabolites in question accumulated. The degradation of glycogen and the accumulations of glucose and lactic acid were noticeably faster in winter than in summer. These findings suggest that ascidian adapts enzymatically to environmental changes, especially to attain certain catalytic efficiency in winter and, as a result, that high enzymatic activities in winter can enhance rapid postmortem changes in the ascidian muscle.