Fructokinase (/fruc•to•ki•nase/ ki´nas, also known as D-fructokinase or D-fructose (D-mannose) kinase,DBGET ENZYME: 2.7.1.4
. Retrieved 2007-05-06 is an enzyme () of the

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

, and

kidney cortex The renal cortex is the outer portion of the kidney between the renal capsule and the renal medulla. In the adult, it forms a continuous smooth outer zone with a number of projections ( cortical columns) that extend down between the pyramids. It ...

. Fructokinase is in a family of enzymes called

transferase A transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved in hundreds of di ...

s, meaning that this enzyme transfers functional groups; it is also considered a

phosphotransferase Phosphotransferases are a category of enzymes ( EC number 2.7) that catalyze phosphorylation reactions. The general form of the reactions they catalyze is: :A-P + B \rightleftharpoons B-P + A Where ''P'' is a phosphate group and A and B are the do ...

(or, frequently, a

kinase In biochemistry, a kinase () is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule don ...

) since it specifically transfers a phosphate group. Fructokinase specifically catalyzes the transfer of a phosphate group from adenosine triphosphate (ATP, the substrate) to fructose as the initial step in its utilization. The main role of fructokinase is in carbohydrate metabolism, more specifically,

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

and fructose metabolism. The reaction equation is as follows: : ATP + D-fructose → ADP + D-fructose 1-phosphate.

Role in plants and bacteria

Fructokinase has been characterized from various organisms such as pea (''Pisum sativum'') seeds,

avocado The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family (Lauraceae). It is native to the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for i ...

(''Persera americana'') fruit, and

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...

(''Zea mays'') kernels, and many more. Specifically, fructokinase may also regulate starch synthesis in conjunction with SS, sucrose synthase, which first metabolizes sink tissue in plant tissues such as in potatoes. 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. In ''

Sinorhizobium meliloti ''Ensifer meliloti'' (formerly ''Rhizobium meliloti'' and ''Sinorhizobium meliloti'') are an aerobic, Gram-negative, and diazotrophic species of bacteria. ''S. meliloti'' are motile and possess a cluster of peritrichous flagella. ''S. meliloti'' ...

'', a common gram-soil bacterium, fructokinase is also used in the metabolism of mannitol and sorbitol, in addition to the metabolism of fructose.

Role in animals and humans

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. 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. Unlike

phosphofructokinase Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis. Function The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes. ...

, fructokinase is not inhibited by ATP.

Diseases

Fructosuria or hepatic fructokinase deficiency is a rare but benign inherited metabolic disorder.WebMD Children's Health - Fructosuria
Retrieved 2007-05-06 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. The disease is mainly characterized by the detection of the abnormal excretion of fructose in the urine through a urinalysis. Fructokinase is needed for the synthesis of glycogen, the body's form of stored energy, from fructose. The presence of fructose in the blood and urine may lead to an incorrect diagnosis of diabetes mellitus. Biochemical abnormalities that may lead to the eventual diagnosis of fructosuria are hepatic fructokinase deficiency, levulosuria and ketohexokinase deficiency.

References

External links

* {{Portal bar, Biology, border=no EC 2.7.1

Role in plants and bacteria

Role in animals and humans

Diseases

See also

References

External links