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Evidence is presented for the existence of many different systems of proteolytic enzymes in human skeletal muscle. These include the lysosomal system of cathepsins as well as proteinases and peptide hydrolases that are optimally active at neutral and alkaline pH ranges. The majority of proteolytic enzymes examined are found to show increased activity in dystrophic human muscle. Moreover, a high initial rise is observed in cathepsin B1, a thiol-dependent endopeptidase of lysosomes, and in dipeptidyl peptidase IV, a membrane-associated peptidase. In addition, a calcium-activated neutral proteinase is found to be significantly elevated in muscle from patients with Duchenne dystrophy. The possible roles of these proteinases in intracellular protein catabolism and muscle wasting are discussed.

Three new cases of carnitine palmityl transferase deficiency are described. The syndrome consists of recurrent attacks of muscle cramps, weakness, malaise, and myoglobinuria. These attacks are especially likely to occur during prolonged exercise after fasting, eating a high-fat diet, or during cold weather. Occasionally after fasting alone, spontaneous muscle breakdown may occur. One patient studied in detail was excessively slow in producing ketones when he fasted. His mylagias and weakness appeared to be alleviated by beta-hydroxybutyrate. Of eight other patients thought to have idiopathic recurrent myoglobinuria, three were found to have myophosphorylase deficiency, whereas five did not have deficiency of either enzyme. Carnitine palmityl transferase deficiency may be more common than previously supposed, may be in part amenable to dietary therapy, can be easily distinguished from myophosphorylase deficiency, and may provide insight into the metabolism of fatty acids and ketone bodies as well as energy requirements of skeletal muscle.

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