Abstract
μ-Calpain quickly split the α-connectin in myofibrils into β-connectin, and then produced a 1700-kDa component. Cathepsin D also split α-connectin into β-connectin, further degrading it to fragments smaller than the 1700-kDa component with increasing incubation time. The action of cathepsin D on the connectin molecule was distinctly different from that of μ-calpain in terms of the splitting rate and manner. When freshly excised muscle was exposed to a temperature of 37°C, complete disappearance of connectin (α, βand 1700-kDa component) was observed within 36h. In contrast, at 2°C, about 75% of connectin was retained as β-form even after 3 weeks. The present data suggest that the degradation of connectin in muscle might be caused by μ-calpain in the early stage of aging, and then with time, this action is replaced by m-calpain or cathepsin D. However, the possibility of other intrinsic proteases participating in the degradation of connectin still remains.
