Major proteolytic pathways in skeletal muscle

Abstract

Skeletal muscle contains multiple proteolytic systems that are presumably responsible for the breakdown of specific proteins. Three major proteolitic pathways operate in skeletal muscle, although such a simple division is too simplified. The best known proteolytic system is the lysosomal pathway. Lysosomes are particularly abundant in liver, and they are not involved in the degradation of myofibrillar proteins. The Ca²⁺-dependent proteolytic process does not contribute significantly to overall proteolysis in muscles from control and catabolic animals. In fact, there is now growing evidence that calpains do not play a major role in general turnover of intracellular protein, but are involved in limited proteolysis of some specific target proteins. Fagan et al. (1987) demonstrated that skeletal muscle also contains a soluble ATP-ubiquitin-dependent proteolytic system.There is more and more evidence that ATP-ubiqutin-dependent proteolitic system has a key role in muscle protein breakdown.