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Hexose metabolism in pancreatic islets
Author(s) -
SENER Abdullah,
GIROIX MarieHélène,
MALAISSE Willy J.
Publication year - 1984
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1984.tb08453.x
Subject(s) - fructose , hexokinase , islet , pancreatic islets , fructokinase , medicine , phosphorylation , fructolysis , endocrinology , mannose , hexose , biochemistry , biology , chemistry , metabolism , insulin , glycolysis , enzyme
Fructose, like glucose, rapidly equilibrates across the plasma membrane of pancreatic islet cells, but is poorly metabolized and is a weak insulin secretagogue in rat pancreatic islets. A possible explanation for such a situation was sought by investigating the modality of fructose phosphorylation in islet homogenates. Several findings indicated that the phosphorylation of fructose is catalyzed by hexokinase, but not fructokinase. First, at variance with the situation found in liver homogenates, the phosphorylation of fructose in the islet homogenate was unaffected by K + and inhibited by glucose, mannose, glucose 6‐phosphate or glucose 1,6‐bisphosphate. Second, the K m for fructose was much higher in islets than in liver. Third, in islet homogenates the K m and V max for fructose were much higher than those for glucose or mannose phosphorylation, at low aldohexose concentrations, in good agreement with the properties of purified hexokinase. In intact islets fructose augmented the islet content in glucose 6‐phosphate sufficiently to cause marked inhibition of its own rate of phosphorylation. These findings may account, in part at least, for the low rate of fructose utilization by rat pancreatic islets.

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