muscles - Does a piezoelectric organic substance exist?

I don't know if it would contract by the amount that you are after, but bone (which has both organic and inorganic components) is piezoelectric.

For an overview, see http://silver.neep.wisc.edu/~lakes/BoneElectr.html.

They suggest that two different mechanisms are responsible for these effects: classical piezoelectricity due to the molecular asymmetry of collagen in dry bone, and fluid flow effects, possibly streaming potentials in wet bone.