Fructokinase
| Fructokinase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 Fructokinase dimer, Bacillus subtilis | |||||||||
| Identifiers | |||||||||
| EC no. | 2.7.1.4 | ||||||||
| CAS no. | 9030-51-7 | ||||||||
| Databases | |||||||||
| BRENDA | enzyme data | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | enzyme entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| Rhea | reactions | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| |||||||||
Fructokinase (/fruc•to•ki•nase/ [-ki´nas]), also known as D-fructokinase or D-fructose (D-mannose) kinase,[1] is an enzyme (EC 2.7.1.4) of the liver, intestine, and kidney cortex. Fructokinase is in a family of enzymes called transferases, meaning that this enzyme transfers functional groups; it is also considered a phosphotransferase (or, frequently, a kinase) since it specifically transfers a phosphate group.[1] Fructokinase specifically catalyzes the transfer of a phosphate group from adenosine triphosphate (ATP, the substrate) to fructose as the initial step in its metabolism.[1] The main role of fructokinase is in carbohydrate metabolism, more specifically, sucrose and fructose metabolism.
Role in plants and bacteria
[edit]Fructokinase has been characterized from various organisms, such as pea (Pisum sativum) seeds, avocado (Persera americana) fruit, and maize (Zea mays) kernels, and many more.[2]
Specifically, fructokinase may also regulate starch synthesis in conjunction with sucrose synthase.[2] There are also two divergent fructokinase genes that are differentially expressed and which also have different enzymatic properties such as those found in tomatoes. In tomatoes, fructokinase 1 (Frk 1) mRNA is expressed at a constant level during fruit development. However, fructokinase 2 (Frk 2) mRNA has a high expression level in young tomato fruit but then decreases during the later stages of fruit development. Frk 2 has a higher affinity for fructose than Frk 1 but Frk 2 activity is inhibited by high levels of fructose, whereas Frk 1 activity is not.[2]
In Sinorhizobium meliloti, a common gram-soil bacterium, fructokinase is also used in the metabolism of mannitol and sorbitol, in addition to the metabolism of fructose.[3]
Role in animals
[edit]In human liver, purified fructokinase, when coupled with aldolase, has been discovered to contribute to an alternative mechanism to produce oxalate from xylitol. In coupled sequence, fructokinase and aldolase produce glycolaldehyde, a precursor to oxalate, from D-xylulose via D-xylulose 1-phosphate.[4]
In rat liver cells (hepatocytes), GTP is also a substrate of fructokinase. It can be used at a substantial rate by fructokinase. In these isolated hepatocytes, in vivo, when the concentration of ATP falls to about 1 millimole in a short time interval, GTP becomes an important substrate under these specific conditions.[5] Unlike phosphofructokinase, fructokinase is not inhibited by ATP.[6]
Synthesis
[edit]The reaction equation to form fructokinase is:
Diseases
[edit]Fructosuria or hepatic fructokinase deficiency is a rare but benign inherited metabolic disorder.[7] This condition is caused by a deficiency of fructokinase in the liver. Affected individuals usually display a large blood fructose concentration after the ingestion of fructose, sucrose or sorbitol.[8]
See also
[edit]References
[edit]- 1 2 3 DBGET ENZYME: 2.7.1.4 Archived 27 September 2007 at the Wayback Machine. Retrieved 2007-05-06
- 1 2 3 Odanaka S, Bennett AB, Kanayama Y (July 2002). "Distinct physiological roles of fructokinase isozymes revealed by gene-specific suppression of Frk1 and Frk2 expression in tomato". Plant Physiol. 129 (3): 1119–26. doi:10.1104/pp.000703. PMC 166506. PMID 12114566.
- ↑ Gardiol A, Arias A, Cerveñansky C, Gaggero C, Martínez-Drets G (October 1980). "Biochemical characterization of a fructokinase mutant of Rhizobium meliloti". J. Bacteriol. 144 (1): 12–6. doi:10.1128/jb.144.1.12-16.1980. PMC 294576. PMID 6252186.
- ↑ James HM, Bais R, Edwards JB, Rofe AM, Conyers AJ (February 1982). "Models for the metabolic production of oxalate from xylitol in humans: a role for fructokinase and aldolase". The Australian Journal of Experimental Biology and Medical Science. 60 (Pt 1): 117–22. doi:10.1038/icb.1982.11. PMID 6284103.
- ↑ Phillips MI, Davies DR (15 June 1985). "The mechanism of guanosine triphosphate depletion in the liver after a fructose load. The role of fructokinase". Biochem. J. 228 (3): 667–71. doi:10.1042/bj2280667. PMC 1145036. PMID 2992452.
- ↑ Samuel, Varman T (February 2011). "Fructose induced lipogenesis: from sugar to fat to insulin resistance". Trends in Endocrinology and Metabolism. 22 (2): 60–5. doi:10.1016/j.tem.2010.10.003. PMID 21067942. S2CID 33205288.
- ↑ WebMD Children's Health – Fructosuria Archived 9 May 2007 at the Wayback Machine. Retrieved 2007-05-06
- ↑ Asipu A, Hayward BE, O'Reilly J, Bonthron DT (September 2003). "Properties of normal and mutant recombinant human ketohexokinases and implications for the pathogenesis of essential fructosuria". Diabetes. 52 (9): 2426–32. doi:10.2337/diabetes.52.9.2426. PMID 12941785.
External links
[edit]- Fructokinases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
