Mannoheptulose

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.[1]

d-Mannoheptulose
Names
IUPAC name
d-Manno-hept-2-ulose
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.020.723
UNII
Properties
C7H14O7
Molar mass 210.182 g·mol−1
Density 1.7 g cm−3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Inhibition of hexokinases

Mannoheptulose is a competitive and non-competitive inhibitor of both hexokinase and the related liver isozyme glucokinase.[2] [3] [4] 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.[5][6] However, while mannoheptulose is suggested to affect the energy balance of adult dogs, independent of dosage and physical activity, research disagrees whether it significantly alters energy expenditure in dogs.

Inhibition of insulin secretion

Mannoheptulose has been reported to inhibit insulin secretion from pancreas.[7] 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,[1] avocados.[8][1] fig,[1] and the primrose.[1] Heptoses can make up over a tenth of the tissue dry weight of the avocado tree.[1] Though the carbohydrate is thought to be produced during photosynthesis[8] the precise biological pathway for the synthesis of mannoheptulose was unknown as of 2002.[1] Like other sugars it is transported in the phloem.[8][1]

References
  1. Liu, Xuan; Sievert, James; Arpaia, Mary Lu; Madore, Monica A. (2002-01-01). "Postulated Physiological Roles of the Seven-carbon Sugars, Mannoheptulose, and Perseitol in Avocado". Journal of the American Society for Horticultural Science. 127 (1): 108–114. doi:10.21273/JASHS.127.1.108. Retrieved 2018-06-26.
  2. Sir Philip John Randle; Haldane "Hal" G. Coore (1 April 1964). "Inhibition of glucose phosphorylation by mannoheptulose". Biochemical Journal. 91 (1): 56–59. doi:10.1042/bj0910056. PMC 1202814. PMID 5319361.
  3. Olivier Scruel; Chantal Vanhoutte; Abdullah Sener; Willy Jean Malaisse (1998-10-01). "Interference of D-mannoheptulose with D-glucose phosphorylation, metabolism and functional effects: Comparison between liver, parotid cells and pancreatic islets". Molecular and Cellular Biochemistry. 187 (1/2): 113–120. doi:10.1023/A:1006812300200. PMID 9788748.
  4. Dai, N; Schaffer, A; Petreikov, M; Shahak, Y; Giller, Y; Ratner, K; Levine, A; Granot, D (1999). "Overexpression of Arabidopsis hexokinase in tomato plants inhibits growth, reduces photosynthesis, and induces rapid senescence". The Plant Cell. 11 (7): 1253–66. doi:10.1105/tpc.11.7.1253. PMC 144264. PMID 10402427.
  5. McKnight, Leslie; Root-McCraig, Jared; Wright, David; Davenport, Gary; France, James; Shoveller, Anna Kate (2015). "Dietary Mannoheptulose Does Not Significantly Alter Daily Energy Expenditure in Adult Labrador Retrievers". PLoS ONE. 10 (12): e0143324. doi:10.1371/journal.pone.0143324. PMC 4684352. PMID 26656105.
  6. McKnight, Leslie; Eyre, Ryan; Gooding, Margaret; Davenport, Gary; Shoveller, Anna Kate (2015). "Dietary Mannoheptulose Increases Fasting Serum Glucagon Like Peptide-1 and Post-Prandial Serum Ghrelin Concentrations in Adult Beagle Dogs". Animals. 5 (2): 442–454. doi:10.3390/ani5020365. PMC 4494402. PMID 26479244.
  7. Lucke, Christoph; Kagan, Avir; Adelman, Neil; Glick, Seymour (1972). "Effect of 2-Deoxy-D-Glucose and Mannoheptulose on the Insulin Response to Amino Acids in Rabbits". Diabetes. 21 (1): 1–5. doi:10.2337/diab.21.1.1. PMID 5008084.
  8. Tesfay, Samson Zeray; Bertling, Isa; Bower, John P. (March 2012). Cowan, Ashton Keith (ed.). "D-mannoheptulose and perseitol in 'Hass' avocado: Metabolism in seed and mesocarp tissue". South African Journal of Botany. 79: 159–165. doi:10.1016/j.sajb.2011.10.006.
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