63: Mechanism of fructose-induced hyperuricemia

Abstract

To investigate the mechanism whereby fructose provokes a loss of total, adenine nucleotides, the kinetics of purified rat liver AMP-aminohydrolase was studied with a new method based on the separation by column chromatography of radioactive IMP formed from [14C] AMP. The sensitivity of this method greatly facilitated the study of the enzyme in the presence of physiological concentrations of its substrate (0.2mM) and effectors (3mM for ATP. 0.5mM for GTP, 5mM for Pi). ATP 3mM increased the enzyme activity 200-fold due to a change of the kinetics from sigmoidal to hyperbolic. The inhibitory effect of Pi on the ATP-activated enzyme became only apparent at ATP concentrations below 1mM or if 0.3 to 0.5mM of. the inhibitor GTP was also present. At physiological concentrations of substrate and effectors, the combined inhibitory effects reached 95%. Within 10 sec. after the administration of fructose (2.5 mg/g I.V.) to mice, the concentration of Pi decreased abruptly, reaching 50% of its control value at 30 sec. A similar decrease of the level of GTP was found. The concentration of ATP declined progressively, down to 1/2-1/3 of its normal value at 2 min. These findings may explain the transient purine catabolism observed in these conditions since the decrease of the inhibitors becomes offset by the depletion of the activator.