Arylamidase and cathepsin-A activity of normal and dystrophic human muscle.

Human skeletal muscle homogenate has been shown to contain enzymes that catalyze the hydrolysis of L-leucyl p-nitroanilide and carbobenzoxyglutamyl-L-tyrosine, known substrates, respectively, for arylamidase and cathepsin A. The muscle arylamidase was found to be inhibited by p-chloromercuribenzoate. Addition of Co2+ resulted in slight stimulation of its activity. Neither ethylenediamine tetraacetate nor thiol compounds had any appreciable effect on the enzyme. When compared to controls, no significant differences in muscle arylamidase levels were observed in patients with muscular dystrophies and certain selected neuromuscular diseases. Cathepsin A was, however, increased in muscles moderately affected by muscular dystrophy and denervating diseases.