Calpains may potentially contribute to
myofibrillar cleavage (46), although skeletal muscle proteolysis initiation is most likely instigated by caspase 3, a cysteine protease most notably involved in apoptosis (47).
As such, it appears that the insulin / IGF - PI 3K pathway not only regulates
myofibrillar cleavage through caspase 3, but also the ubiquitylation of the resulting protein fragments via modification of ubiquitin - ligase expression.