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.

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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.