This property is maintained at a wide range of frequencies in an insect protein containing many dityrosine and trityrosine crosslinks. Both a “series” and a “parallel” component with this property are described in Hill’s three element model. Worm-like chains such as DNA inherently have an entropic form of this property, while electrostatic interactions within P·E·V·K regions cause a common example of this property's enthalpic form. This property is conferred by the I-band of the giant protein (*) titin (“TAI-tin”). Deficiencies (-5[1])in alpha-1 antitrypsin lead to breakdown of tissue with this property in the lungs, which may cause COPD. Fibrils of collagen, (10[1])fibronectin and a protein named for this property (10[1])are a primary component of the extracellular matrix. For 10 points, name this property of proteins that return to their original length after being stretched. (10[1])■END■