Aquaporin

Aqvaporin is an integral membrane protein regulating water flow across the membrane.

Function mechanism
Regardless of the temperature, water passes through the pores in membrane integral proteins - porins. These water channels are selective for the passage of water, neither solutes nor small molecules pass through them ( urea has its own specific channel).

Some of these channels are controlled chemically, for others the regulation is not yet known.

High specificity is achieved with a channel diameter of 0.2 nm (not even H+, OH- does not pass through). Water passes through a continuous stream of 2-4.109 molecules per second.

Structure

 * Molecular weight 30 kDa;
 * 6 hydrophobic sections (domains);
 * molecules form tetramers (water passes through each molecule separately);
 * 10 types of aquaporin H (AQP0–AQP9);

Occurrence
Their permeability is in many cases controlled by vasopressin (AQP2).