Control of lens glycolysis

Abstract

1. 1. The calf-lens phosphofructokinase (ATP: d-fructose-6-phosphate i-phosphotransferase, EC 2.7.1.11) was isolated and purified 86 fold. It was found that ATP inhibits lens phosphofructokinase at a concentration above 0.25 mM. Cyclic AMP was the most effective in releasing the inhibition of phosphofructokinase by glucose 6-phosphate. 2. 2. The calf-lens hexokinase (ATP: d-hexose 6-phosphotransferase, EC 2.7.1.1) is susceptible to inhibition by low levels of glucose 6-phosphate. The inhibitory effect of glucose 6-phosphate can be partially counteracted by increasing concentrations of inorganic phosphate. 3. 3. The normal content of ATP and glucose 6-phosphate in the lens are at levels where considerable degree of inhibition would be exerted on the two enzymes, hexokinase and phosphofructokinase. 4. 4. The levels of the glycolytic intermediates in the lens were measured after incubation under aerobic conditions at 5.5, 10 and 15 mM glucose. Increasing the availability of glucose raised the intracellular glucose, but the levels of sugar phosphates and the production of lactate remained unchanged. 5. 5. Increasing the availability of glucose did, however, stimulate the lens sorbitol pathway. Increasing levels of sorbitol were found in the lenses incubated at the 3 different concentrations of glucose.