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

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 Ca2+, and a large increase of ATPase over a narrow range of Ca2+ concentration. Flight muscle had a greater ATPase in the absence of Ca2+ but showed a much smaller increase over a wider range of Ca2+ 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 Ca2+, and abolished the Ca2+-activation, in both flight and leg-muscle preparations from the water-bug; addition of ‘native tropomyosin5 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.