Cotransporter

Cotransporters are a subcategory of membrane transport proteins (transporters) that couple the favorable movement of one molecule with its concentration gradient and unfavorable movement of another molecule against its concentration gradient.

They enable coupled or cotransport (secondary active transport) and include antiporters and symporters.

In general, cotransporters consist of two out of the three classes of integral membrane proteins known as transporters that move molecules and ions across biomembranes.

Uniporters are also transporters but move only one type of molecule down its concentration gradient and are not classified as cotransporters.

Some studies show that cotransporters can function as ion channels, contradicting the classical models.

The glucose transporter system was first hypothesized by Dr. Robert K. Crane in 1960, this is discussed later in the article.

[2][3][needs copy edit] Dr. Robert K. Crane, a Harvard graduate, had been working in the field of carbohydrate biochemistry for quite some time.

His experience in the areas of glucose-6-phosphate biochemistry, carbon dioxide fixation, hexokinase and phosphate studies led him to hypothesize cotransport of glucose along with sodium through the intestine.

Pictured right is of Dr. Crane and his drawing of the cotransporter system he proposed in 1960, at the international meet on membrane transport and metabolism.

[4] Antiporters and symporters both transport two or more different types of molecules at the same time in a coupled movement.

The AE1 antiporter is essential in the removal of carbon dioxide waste that is converted to bicarbonate inside the erythrocyte.

SGLT1 is an electrogenic transporter as the sodium electrochemical gradient drives glucose uphill into the cells.

They are also found across the epithelial cells of renal proximal tubule and of the small intestine.

It transfers inorganic phosphate into cells through active transport with the help of a Na+ gradient.