1. 1. The effects of dietary fructose, sucrose, glucose, casein and fasting upon the activity of several glycolytic enzymes [fructokinase (ketohexokinase, EC 2.7.1.3), hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), glucokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.2), Fru-I-P aldolase (ketose-I-phosphate aldehyde-lyase, EC 4.1.2.7), Fru-I,6-P2 aldolase (fructose-I,6-diphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13) and aldose reductase (alditol:NADP+ oxidoreductase, EC 1.1.1.21)] were studied in the jejunum of rats. 2. 2. Individual sugars (glucose, sucrose and fructose) have specific carbohydrate effects on certain jejunal glycolytic enzymes. Fructose had a specific adaptive effect upon fructokinase and Fru-I-P aldolase, while glucose exerted its adaptive effect upon hexokinase and glucokinase. The addition of calories in the form of casein to fasted rats caused a non-specific increase in the activity of all jejunal glycolytic enzymes studied. 3. 3. Changes in rat jejunal glycolytic enzymes due to diet reflect those in rat liver. 4. 4. The ratio of Fru-I,6-P2/Fru-I-P adolase activities in the liver activities was close to 1.0 for all diets whereas in the jejunum the ratio of activities is altered by diet. The fact that the jejunal activity ratio was lower than I in fructose-fed rats suggests that the intestine may contain an aldolase with different properties from those in other tissues. © 1968.
