Mannoheptulose is a heptose, a monosaccharide with seven carbon atoms, and a ketose, with the characteristic carbonyl group of the carbohydrate present on a secondary carbon (functioning as a ketone group). The sugar alcohol form of mannoheptulose is known as perseitol.
Inhibition of hexokinases
Mannoheptulose is a competitive and non-competitive
enzyme inhibitor of both
hexokinase and the related liver
isozyme glucokinase.
By blocking the enzyme hexokinase, it prevents
glucose phosphorylation, the first step in the fundamental biochemical pathway of
glycolysis. As a result, the breakdown of glucose is inhibited.
Because of its inhibition of glycolysis in vitro, it has been investigated as a novel nutraceuticals for weight management for dogs.
Inhibition of insulin secretion
Mannoheptulose has been reported to inhibit insulin secretion from pancreas.
This inhibition occurs because when mannoheptulose is present the glycolysis is inhibited (because there is no production of glucose-6-P) therefore no increase in ATP concentration which is required to close the KATP channel in the beta cells of the pancreas causing a diminution of calcium entry and insulin secretion.
Natural occurrence
Mannoheptulose is naturally occurring in
alfalfa,
,
,
and the
Primula vulgaris.
Heptoses can make up over a tenth of the tissue dry weight of the avocado tree.
Though the carbohydrate is thought to be produced during photosynthesis
the precise biological pathway for the synthesis of mannoheptulose was unknown as of 2002.
Like other sugars it is transported in the
phloem.
