Abstract
The metabolic intermediate concentrations and enzyme activities were determined in the hepatopancreas of carp Cyprinus carpio fed for 30 days with diets high in protein, lipid, and carbohy-drate. The effect of physiological concentrations of the intermediates on the activity of purified phos-phofructokinase (PFK) was also investigated. The dietary treatments induced slow but marked changes in activities of hepatopancreatic enzymes. This suggested an enzyme induction in the fish hepatopancreas but could not account for the rapid response of body composition to the dietary treat-ments. Each concentration of ATP, ADP, AMP, G1P, G6P, F6P, and FDP in the hepatopancreas ranged from 10-3M to 10-5M, corresponding to the Km values for many glycolytic enzymes such as PFK. These physiological concentration ranges of ATP, AMP, F6P, and citrate markedly and reasonably affected in vitro PFK activity. The results suggest that in vivo glycolytic activity can be regulated not only by enzyme induction but also by PFK activity without enzyme induction through changes in the physiological concentrations of metabolic intermediates as substrate and effector.
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