Skeletal muscle is not only important in animal locomotion, but also constitutes a major metabolic store of protein that can be quickly mobilized when dietary intake is insufficient to meet an animal's nutritional needs. In addition, muscle atrophy can be induced by disuse, nerve injury, and disease. In some disuse, such as muscular dystrophy, wasting is so severe that individual dies. The intracellular regulation of protein breakdown in any animal poorly understood. The crustacean claw muscle provides a favorable model system for elucidating proteolytic mechanisms. During each intermolt cycle, the claw muscle undergoes a sequential atrophy and restoration, in which protein content decreases 40% during the premolt period and is resynthesized following molt. Atrophy apparently facilitates withdrawal of the pair of large claws at the time the shell is shed. Protein degradation appears to be mediated by five enzymes: four calcium- dependent proteinases (CDPs) and a multicatalytic proteinase (MCP). The enzymes are active a neutral pH and degrade the contractile proteins of muscle. This proposal examines the regulation of intracellular proteolysis in a muscle that resembles, both morphologically and biochemically, vertebrate skeletal muscle. Biochemical and molecular biological techniques are used to isolate and characterize two proteinases. These studies will yield new and basic information on the regulation of proteolytic processes common to all animal cells.
