INTESTINAL METABOLISM OF FRUCTOSE

The metabolism of fructose by the small intestine can be analyzed in terms of the following scheme: 1) hydrolysis of fructose containing saccharides especially sucrose; 2) movement of fructose into the intestinal cell; 3) transformation of fructose into glycolytic metabolic intermediates; 4) formation of fructose from glucose via sorbitol; 5) adaptive regulation of fructose metabolizing enzymes; 6) adaptive responses of other enzymes to fructose. The hydrolysis of sucrose is dependent upon the brush border enzyme sucrase which shows an adaptive response to sucrose diets. The entrance of fructose into the small intestine and the intermediary metabolism of fructose is reviewed. Fructose metabolizing enzymes, fructokinase and fructose-1-phosphate aldolase, are regulated by the presence or absence of fructose, folic acid and drugs. Fructose causes adaptive changes in small intestine glycolytic enzymes and decreases the gluconeogenic enzyme fructose-1,6-diphosphatase. Actinomycin D inhibits the adaptive effect of fructose on glycolytic enzymes which suggests that fructose acts via the protein synthetic mechanism.