Abstract
1. The regulation of fructose metabolism was investigated in rat liver using a non-recirculating perfussion system. 2. 1. At 25 mM fructose the rate of fructose uptake was 6.6 μmoles·min −1·g −1. Calculated per whole liver the rate of fructose uptake was independent of the nutritional state, whereas the rate of fructose uptake calculated per g liver increased 25% by 48 h fasting. 3. 2. The rate of fructose uptake was diminished in the first (20 min) period after addition of fructose. Glucose up to 25 mM did not significantly decrease the rate of fructose uptake indicating a minor contribution of hexokinase (ATP: d-hexone 6-phosphotransferase, EC 2.7.1.1) in phosphorylating fructose. The rate of fructose uptake was increased 25% by increasing the P i concentration from 1 to 5 mM in the affluent medium. Ethanol caused a decreased in the rate of fructose phosphorylation. This was counterpoised by an increased rate of sorbitol production. 4. 3. 5 mM P i caused an increased rate of O 2 uptake with and without fructose, and the concentration of ATP during steady-state fructose metabolism was increased 25% which was enough to account for the increase in the rate of fructose uptake (ketohexokinase (ATP: d-fructose 1-phosphotransferase, EC 2.7.1.3) K m with ATP , 0.9 mM). 5. 4. At a high NAD redox level which was seen in the initial 10-min period after addition of fructose and after addition of ethanol, glycerol and sorbitol were released from the liver. The kinetics of sorbitol release reflected the intracellular fructose concentration. 6. 5. In livers of fed but not of fasted animals the release of glucose was inhibited in the initial 10-min period after addition of fructose. The inhibition is related to an increased inhibition of fructose 1-phosphate aldolase and fructose diphosphatase in the fed animal.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call