Abstract
It has been postulated that inhibition of LP plays a significant role in the fructose-induced hypoglycemia of HFI. To test this hypothesis weanling mice were injected i.p. with 30 m-moles/kg of fructose or saline of equal osmolality. Although liver glucose levels did not fall the findings are relevant to the understanding of the pathophysiology of HFI. 20 min after fructose injection, fructose and fructose-1-P (F-1-P) levels were 21.4 ± 2.9 and 10.6 ± 0.9 m-moles/kg respectively. ATP and Pi were reduced 50%, to 1.36 m-moles/kg and 2.07 m-moles/kg, p = 0.001. At the same time LP was reduced 48% (p = 0.002). This finding suggest a shift to the inactive form of the enzyme. To mimic the in vivo situation LP in normal liver homogenate was measured in the presence of the concentrations of Pi and F-1-P found after fructose injection. The activity of the enzyme was reduced 88% by these additions (from 5.9 to 0.74 μ-moles/g min, p 0.001). Therefore, it appears that in vivo the activity of liver phophorylase is reduced by two mechanisms, a conversion of the active to the inactive form, and an inhibition of the remaining active enzyme by the elevated F-1-P and reduced Pi levels.
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Thurston, J., Jones, E. & Dodge, P. Decrease and inhibition of liver phosphorylase (LP) after fructose: An experimental model for the study of hereditary fructose intolerance (HFI). Pediatr Res 5, 392 (1971). https://doi.org/10.1203/00006450-197108000-00087
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DOI: https://doi.org/10.1203/00006450-197108000-00087