Dietary regulation of glycolytic enzymes: III. Adaptive changes in rat jejunal pyruvate kinase, phosphofructokinase, fructosediphosphatase and glycerol-3-phosphate dehydrogenase

Abstract

1. 1. The effects of dietary fructose, glucose, casein and fasting upon the activity of six enzymes involved in carbohydrate metabolism (phosphofructokinase (ATP: d-fructose-6-phosphate 6-phosphotransferase, EC 2.7.1.11), pyruvate kinase (ATP: pyruvate phosphotransferase, EC 2.7.1.40), fructosediphosphatase ( d-fructose-1,6-diphosphate 1-phosphohydrolase, EC 3.1.3.11), glycerol-3-phosphate dehydrogenase ( l-glycerol 3-phosphate: NAD oxidorectase, EC 1.1.1.8), glucokinase (ATP: d-hexose 6-phosphotransferase, EC 2.7.1.2), and hexokinase (ATP: d-hexose 6-phosphotransferase, EC 2.7.1.1)) were studied in the jejunum and liver of rats. 2. 2. Individual sugars (fructose and glucose) have specific carbohydrate effects on certain jejunal glycolytic enzymes. Fructose had a specific adaptive effect upon pyruvate kinase, phosphofructokinase and glycerol-3-phosphate dehydrogenase, while glucose exerted its maximum adaptive effect upon hexokinase and glucokinase. The addition of calories in the form of casein to fasted rats caused a nonspecific increase in the activity of these same enzymes. 3. 3. Fructosediphosphatase activity was highest in the fasted rats and decreased in order on the casein, fructose and glucose diets. The fructosediphosphatase to phosphofructokinase activity ratio was highest in the fasted rats, lower on the casein diet and lowest on glucose and fructose diets. 4. 4. Changes in rat jejunal enzymes due to diet reflect those in rat liver.