The calcium sensitivity of ATP ase activity of myofibrils and actomyosins from insect flight and leg muscles

Publisher Website
Google Scholar
Abstract
Myofibrils and actomyosin suspension were prepared from the fibrillar flight and non-fibrillar leg muscles of the water-bug, Lethocerus maximus, and their ATPase activity measured in solutions of various ionic strength containing MgATP. Leg muscle showed a low ATPase in the absence of Ca$^{2+}$, and a large increase of ATPase over a narrow range of Ca$^{2+}$ concentration. Flight muscle had a greater ATPase in the absence of Ca$^{2+}$ but showed a much smaller increase over a wider range of Ca$^{2+}$ concentration. A similar difference between flight and leg muscle was found in the honey-bee, Apis mellifera, and the beetle, Oryctes rhinoceros, both of which have fibrillar flight muscles, but was not found in the locust, Locusta migratoria, which has non-fibrillar flight muscle. Tryptic digestion raised the ATPase in the absence of Ca$^{2+}$, and abolished the Ca$^{2+}$-activation, in both flight and leg-muscle preparations from the water-bug; addition of 'native tropomyosin' prepared from rabbit muscle partially reversed the effect. These results are discussed in relation to the structural peculiarities and oscillatory mechanical activity of fibrillar flight muscle.