This proposal is designed to further our understanding of unusual contractions in two types of invertebrate muscles. The thick filaments of Limulus muscle shorten, by end-fragmentation, in order to accommodate to the shortest in situ sarcomere length. Molluscan smooth adductors and Mytilus ABRM exhibit tonic contractions: catch, characterized by maintenance of the active state with no energy use. These studies will determine the interactions between core paramyosin and cortical myosin molecules of these thick filaments and define the changes in these interactions during the unusual contractions of these muscles. Monoclonal antibodies to the proteins will be used as probes. Electron microscopy of: protein molecules, synthetic protein aggregates, cores and intact filaments will be used to analyze structural changes. Biochemical assays of protein interactions will define the molecular state characteristic of catch, and the presence of catch in skinned molluscan muscles will be monitored, physiologically.//
