Regulation of liver diphosphofructose phosphatase of the rat and hamster

The regulatory properties of D-fructose-1, 6-diphosphate 1-phosphohydrolase (FDPase, EC 3.1.3.11) derived from livers of the albino rat and the golden Syrian hamster have been studies. The comparative analysis of the kinetics of saturation by fructose-1, l-diphosphate (FDP) and inhibition by FDP and by the allosteric ligand adenosine 5'-monophosphate (AMP) revealed differences that may have physiological implications. The inhibition studies pointed out that liver phosphatase is under a significantly less stringent regulation in the hibernating rodent. The concentration of AMP required to produce a 50 percent inhibition was 549.5 muM at 37 degrees C, 21.4 muM at 10 degrees C, and 9.2 muM at 5 percent C for the rat; 1,122 muM at 37 degrees C, 34.3 muM at 10 degrees C, and 20.4 muM at 5 degrees C for the hamster. Urea (0.67 M) simulates the effect of low temperature, potentiating the AMP inhibition. At 5 degrees C and 4 M urea, 75 percent loss of activity was found for the rat FDPase in contrast to a 25 percent loss for the hamster. At 37 degrees C, 4 M urea had practically no effect on the FDPase of both species.