Kinetic parameters of human and rabbit liver d-fructose 1,6-diphosphate 1-phosphohydrolase determined at 25 and 37°C

Abstract

1. 1. Kinetic parameters of human and rabbit liver d-fructose 1,6-diphosphate 1-phosphohydrolase (EC 3.1.3.11) (FDP-ase) at 25 and 37°C have been determined. 2. 2. K m determined at 25°C were 1.4 μM for human and 1.6 μM for rabbit enzyme; at 37°C, corresponding values were 1.7 and 1.8 μM. 3. 3. Both enzymes are allosterically inhibited by AMP. Respective values of i 0.5 were 7.2 μM for human and 13.2 μM for rabbit at 25°C, and 16.6 μM for human and 27.3 μM for rabbit at 37°C. 4. 4. Fructose 2,6-diphosphate, a potent regulator of gluconeogenesis, is more effective at 25 than at 37°C. K i determined at 25°C was 0.07 μM for human and 0.035 μM for rabbit in comparison with 0.17 μM for human and 0.09 μM for rabbit at 37°C. 5. 5. Affinity of FDP-ase for magnesium is also dependent on temperature. For the human enzyme, K m at 25°C was 226 μM and at 37°C, 176 μM. For the rabbit enzyme, corresponding values were 256 and 240 μM. 6. 6. Both enzymes are activated by KCl. Determined values of A 0.5 were 91 mM for human, and 50 mM for rabbit enzyme at 25°C, and 129 mM for human and 100 mM for rabbit enzyme at 37°C.