Mechanical Properties and Control of Nonmuscular Catch in Spine Ligaments of the Sea Urchin, Strongylocentrotus Franciscanus

ABSTRACT Catch was induced in the spine ligaments of Strongylocentrotus franciscanus (Agassiz) (surrounding muscle and nervous tissue removed) by mechanical agitation. When the catch mechanism is set, the tensile stiffness of urchin ligament can change by nearly an order of magnitude and approaches that of vertebrate tendon. Deflection of a spine in catch through an angle of more than 10° damages the catch mechanism. Setting of catch depends on extracellular calcium. Transglutaminase inhibitors (cadaverine and putrescine) prevent the setting of catch. A model involving Ca-dependent activation of a transglutaminase-like enzyme is discussed as a possible basis for the setting of catch by crosslinking collagen fibrils.