CONTRACTION IN GLYCERINATED MYOFIBRILS OF AN INSECT (ORTHOPTERA, ACRIDIDAE).
The A substance of glycerol-treated myofibrils of the femoral muscles of the locust Gastrimargus musicus (Fabr.), removed by a salt solution of high ionic strength, has the properties of actomyosin. A phase contrast study of these fibrils, contracted by the addition of ATP, has revealed that the A bands of most myofibrils shorten during contraction. Changes in density within the A band lead to the formation of C(m) and C(z) bands while I bands are still present. The A band region between the contraction bands is of much lower density than it is in the uncontracted fibril. During contraction in some fibrils the I bands disappeared and the A bands remained unchanged in length until contraction bands appeared. These results have been interpreted in terms of coiling and stretching of the thick filaments of the sarcomere.
Division of Entomology, Commonwealth Scientific and Industrial Research Organisation, Canberra, Australia.
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Gilmour
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Robinson