Control of muscle proteolysis in insects

In metamorphosing insects entire muscle masses may be destroyed within a matter of hours. The breakdown is controlled by neural and endocrine mechanisms; more recent evidence suggests tha a decrease in availability of oxygen occurs shortly prior to the onset of rapid involution. There are at least two phases of lysis, the slower first phase occurring in functioning muscle. Electron microscopic evidence suggests an early change in the morphology of the Z-line, followed several hours later by dissolution of the myofilaments. During the phase of rapid involution, a 60,000--70,000 dalton protein appears transiently in the tissue. Current evidence suggests that the rate-limiting step in the degradation of myosin is reduction to this presumed fragment; beyond this point, the muscle proteins are rapidly degraded to amino acids or small peptides.