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 metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...
,
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 tract is the largest of the body's systems, after the cardiovascular system. T ...
, and
kidney cortex. Fructokinase is in a family of enzymes called
transferase
In biochemistry, 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 ...
s, meaning that this enzyme transfers functional groups; it is also considered a
phosphotransferase
In molecular biology, phosphotransferases are proteins in the transferase family of enzymes ( EC number 2.7) that catalyze certain chemical reactions. The general form of the phosphorylation reactions they catalyze is:
\ce
Where P is a phosphat ...
(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, alligator pear or avocado pear (''Persea americana'') is an evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated in Mesoamerica more than 5,000 years ago. It was priz ...
(''Persera americana'') fruit, and
maize
Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
(''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'', 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.
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.
See also
*
Hepatic fructokinase
*
PFKL
*
PFKM
*
PFKP
*
Glucokinase
Glucokinase () is an enzyme that facilitates phosphorylation of glucose to glucose-6-phosphate. Glucokinase is expressed in cells of the liver and pancreas of humans and most other vertebrates. In each of these organs it plays an important ro ...
*
Hexokinase
A hexokinase is an enzyme that irreversibly phosphorylates hexoses (six-carbon sugars), forming hexose phosphate. In most organisms, glucose is the most important substrate for hexokinases, and glucose-6-phosphate is the most important p ...
References
External links
*
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EC 2.7.1