Quantitation of the pathways of fructose metabolism in normal and fructose-intolerant subjects.

Abstract The pathways of fructose metabolism were studied in 3 subjects with hereditary fructose intolerance (HFI) and 5 subjects from the same kindred who did not have HFI. They were injected with tracer quantities of fructose-6- 14 C and lactate-I- 14 C and then glucose was isolated from each subject's blood and the distribution of the radioactivity among the carbon atoms of the glucose was determined. The incorporation of carbon 1 of the lactate into carbons 3 and 4 of the glucose provided a measure of the extent of triose phosphate isomerization and transaldolase exchange activity. With the use of this measurement and the incorporation of carbon 6 of fructose into carbon 1 of glucose, the extent of phosphorylation of fructose to fructose-6-phosphate compared to fructose-1-phosphate was estimated. In the subjects without HFI, the conversion of fructose to glucose appeared to be solely by way of the fructose-1 -phosphate. These data would also indicate that in these subjects, and presumably in man in general, fructose is not converted by way of sorbitol to glucose in the liver. In the subjects with HFI, the quantity of fructose converted to glucose was decreased. Two of the subjects are estimated to have metabolized 12 to 20 per cent of the fructose by way of fructose-6-phosphate at the load of fructose administered.