GLUT5 is a fructose

Fructose

Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...

 transporter expressed on the apical border of enterocytes in the small intestine

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

. GLUT5 allows for fructose to be transported from the intestinal lumen into the enterocyte by facilitated diffusion

Facilitated diffusion

..Facilitated diffusion is a process of passive transport, facilitated by integral proteins. Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane integral proteins...

 due to fructose's high concentration in the intestinal lumen. GLUT5 is also expressed in skeletal muscle

Skeletal muscle

Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

, testis, kidney, fat tissue, and brain.

Fructose malabsorption

Fructose malabsorption

Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...

 or Dietary Fructose Intolerance is a dietary disability of the small intestine

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

, where the amount of fructose carrier in enterocyte

Enterocyte

Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestines and colon. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase surface area for the digestion and transport of molecules from the intestinal...

s is deficient.

In humans the GLUT5 protein is encoded by the SLC2A5 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.