DNase I interactions with filaments of skeletal muscles

DNase I-actin interactions were studied by electron microscopy and SDS-polyacrylamide gel electrophoresis. Electron micrographs of glycerinated avian pectoralis major muscle fibres treated with 1 mg ml-1 DNase I demonstrated that the Z-lattice was destroyed. The axial filaments of the Z-lattice were still present but were thinner and less ordered than those of control fibres. The small diameter cross-connecting filaments of the Z-lattice were not present in DNase I treated muscle fibres. Treatment with DNase I had the same effect on fast avian skeletal muscles and fast and slow rat skeletal muscles suggesting that the effect was not muscle type or species dependent. The effect of DNase I could be abolished by lowering the DNase I concentration (0.1 mg ml-1 or less). Preincubation of DNase I with purified skeletal muscle actin also abolished the effect of the DNase I. Analysis of the extracts obtained during DNase I treatment by gel electrophoresis demonstrated that substantial quantities of DNase I did not remain associated with the myofibrils. Two proteins, one with an apparent molecular weight of 43 kDa which reacted with an actin antibody and another with an apparent molecular weight of 95 kDa which did not react with an alpha-actinin antibody, were observed in the DNase I extracts. These data suggest that DNase I interacts with protein(s) in the Z-lattice and this interaction causes the subsequent release of actin and other Z-band proteins.