Immunocytochemical localization of a calcium-activated protease in skeletal muscle cells

The 80 000-D subunit of a calcium-activated protease from skeletal muscle was purified to homogeneity using preparative sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and was used to elicit antibody production in rabbits. Antiserum was purified using affinity chromatography to yield a monospecific antibody fraction (anti-80K) directed against the 80 000-D subunit. Localization studies showed that the 80 000-D subunit is present in or near the sarcolemma of cultured myoblasts and sectioned muscle tissue, in discrete areas of the cytoplasm of myoblasts, and in the Z disks of the myofibril. The location of the calcium-activated protease in the cell suggests that the enzyme may be involved in myofibril degradation and in membrane alterations in developing and mature muscle cells.