Forisome

Forisomes are moving proteins occurring in the cells of some plants. Their molecules are about 1-3 µm wide and 10-30 µm long. They expand and contract anisotropically in response to changes of electric field, pH, or concentration of Ca2+ ions. Unlike most other moving proteins, the change is not dependent on ATP.

In the Fabaceae (legume) plants, forisomes function as valves in sieve tubes of the phloem system, by reversibly changing shape between low-volume ordered crystalloid spindles and high-volume disordered spherical conformations. The change from ordered to disordered conformation involves tripling of the protein's volume, loss of birefringence present in the crystalline phase, 120% radial expansion and 30% longitudal shrinkage.

Forisomes have possible applications in nanotechnology and biomimetic smart materials, eg. as valves in microdevices or in smart composite materials.