1. 1. The activities of all the eight enzymes of conversion of fructose to glucose, of all the three key enzymes of glycolysis and of the two dehydrogenases of pentose shunt were determined in proximal and distal mucosa of small intestine. 2. 2. With the exception of hexokinase, all of these enzymes have an activity significantly higher in the proximal than distal mucosa. 3. 3. The gradient along the intestine is particularly important for the three enzymes which are typical for fructose metabolism (ketohexokinase, triokinase and fructose-1-phosphate aldolase), for glucose-6-phosphatase and for phosphofructokinase. 4. 4. The effects of fructose diet on the enzyme activities are compatible with the results, described in other papers, concerning the final products of metabolism. 5. 5. The increase of fructose metabolism appears to result mainly from the stimulation of the activities of ketohexokinase and fructose-1-phosphate aldolase which control all the pathways of ketohexose utilization. 6. 6. The activation of glucose-6-phosphatase, in comparison with the other enzymes which are involved in glucose-6-phosphate metabolism, explains the appearance of the ability to synthesize glucose with fructose as substrate. This enzyme is the only key enzyme of fructose to glucose conversion which responds to fructose feeding in distal mucosa. 7. 7. The activities of hexokinase and phosphofructokinase are not increased by fructose feeding. 8. 8. The activity of pyruvate kinase. the only key glycolytic enzyme which is necessarily implicated when fructose is the substrate, is stimulated but less than the typical enzymes of fructose metabolism. 9. 9. But, because of its quantitative importance, the glycolytic pathway is responsible for the most part of the observed increase of fructose utilization. 10. 10. The responses of pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities to fructose feeding are similar in the two parts of small intestine. 11. 11. The activities of ketohexokinase, triokinase and glucose-6-phosphate isomerase are stimulated only in the proximal small intestine mucosa. 12. 12. The other enzyme activities which are stimulated in proximal segment are also increased in distal segment. 13. 13. All segments of small bowel show adaptive changes to dietary manipulation but not necessarily for all their functions. 14. 14. The gradient of enzyme activities from the proximal to the distal small intestine persists despite dietary modification, but the data do not determine that this gradient is intrinsic or that it is not intrinsic. © 1979.
