EFFECTS OF DIETARY CARBOHYDRATE SOURCES AND LEVELS ON THE ACTIVITIES OF CARBOHYDRATE METABOLIC ENZYMES IN TURBOT

A 34 two-factorial experiment was conducted to investigate the effects of dietary carbohydrate sources (glucose, sucrose and dextrin) and levels (0, 5%, 15% and 28%) on the activities of glycolytic and gluconeogenic enzymes in turbot (Scophthalmus maximus L.). The initial weight of the turbot was (8.060.08) g. Each diet was fed to triplicate groups of turbot in a flow-through water system for 9 weeks. Activities of hexokinase (HK), glucokinase (GK), 6-phosphofructokinase-1 (PFK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1, 6-bisphosphatase (FBPase) were examined. The results showed that hepatic GK and PK activity significantly increased with the increase of dietary carbohydrate level from 0 to 15%. However, there was a lack of further increase of them with 28% of dietary glucose or dextrin. HK and PFK activities were not significantly affected by dietary carbohydrate levels (P 0.05). Activities of FBPase, not PEPCK, were significantly increased by 5% of dietary glucose. Diets supplemented with dextrin depressed hepatic FBPase and PEPCK activity in comparison to that without carbohydrate supplements. Activities of these two enzymes were not significantly affected by dietary sucrose levels (P 0.05). The data suggested that diets supplemented with 15% of glucose or dextrin was effective in enhancing liver glycolytic enzyme activity. Dietary dextrin was more effective than glucose in depressing liver gluconeogenic enzyme activities. Only GK activity was significantly promoted by 28% of dietary sucrose, and no significant effect of dietary sucrose levels on the other enzymes was found.