Nirmal C. Kar

A calcium-activated neutral protease in normal and dystrophic human muscle

Abstract Human skeletal muscle homogenate was found to degrade casein-yellow substrate slowly at neutral pH. This protease activity was maximally stimulated by 1 mM Ca 2+ . A significant increase in the level of Ca 2+ -activated neutral protease was found specifically in muscle of five patients with Duchenne dystrophy and one patient with the Becker form of X-linked dystrophy.

Catalase, superoxide dismutase, glutathione reductase and thiobarbituric acid-reactive products in normal and dystrophic human muscle

The level of thiobarbituric acid-reactive products and the specific activities of catalase and glutathione reductase were significantly higher in muscles from patients with major forms of muscular dystrophies over those of control subjects. Superoxide dismutase activity was not altered in dystrophic muscles. These findings indicate the occurrence in human dystrophic muscles of an increased level of lipid peroxidation and the possible activation of certain enzymes that could conceivably inhibit lipid peroxidation in vivo.

MUSCLE BREAKDOWN AND LYSOSOMAL ACTIVATION (BIOCHEMISTRY)

Muscle tissue levels of lysosomal catheptic enzymes, such as cathepsins D, A, B1, C, and dipeptidyl peptidase II, were measured in control subjects and patients with muscular dystrophies, polymyositis, and certain denervating diseases. The results show that, in general, the activities of these enzymes are increased in muscles of patients with muscular dystrophies and other diseases. The increases in cathepsin D and autolytic activities are not significant until the late stage of the disease process. Cathepsins A, B1, and C are, however, significantly elevated in mildly affected dystrophic and other diseased muscles. Of these catheptic enzymes, cathepsin B1 displays the highest rise at an early stage, suggesting that it may be one of the rate-controlling enzymes of proteolysis. Dipeptidyl peptidase II is increased slightly in dystrophic and other myopathic muscles but is unchanged in denervated muscle. These data clearly implicate the lysosomal group of proteinases as largely responsible for mediating muscle breakdown in the muscular dystrophies and certain other muscle and neuromuscular diseases in man.

Acid hydrolases in normal and diseased human muscle

The activities of acid phosphatase and β-acetylglucosaminidase in muscles from normal persons and from patients with various muscular and neuromuscular diseases have been determined. They are normal in all minimally abnormal muscles irrespective of their different disease etiologies. Increased amounts of these enzymes are only found in the severely deranged muscles obtained from patients with Duchenne muscular dystrophy, other dystrophies, polymyositis, spinal muscular atrophy and in other myopathies. These results suggest that these enzymes are involved in muscle degeneration in humans.

Muscle adenylic acid deaminase activity: Selective decrease in early‐onset Duchenne muscular dystrophy

Pseudohypertrophic muscular dystrophy (Duchenne type) is a progressive primary myopathy inherited as an X-linked recessive trait. The initial genetic aberration remains unknown but may he an intrinsic metabolic lesion of the muscle fibers themselves. Many enzymes are altered in muscle in Duchenne dystrophy hut none is specific.’ i2 Pennington3 first observed that the mean muscle adenylic acid (AMP) deaminase activity was lowered t o about onefourth of normal in five patients with Duchenne dystrophy. The significance of these findings could not he assessed in absence of data on the activity of the enzyme in muscles from patients with other forms of muscular dystrophy, related myopathies, or neuropathies. In this study we measured the activity of this enzyme in muscle from patients with other neuromuscular diseases and showed that AMP deaminase activity of muscle was selectively affected in early-onset Duchenne dystrophy. Creatine kinase of muscle was assayed concurrently for comparison.

Dipeptidyl peptidases in human muscle disease

With the use of selective inhibitors of arylamidase, four dipeptyl peptidases (I, II, III, and IV) capable of hydrolyzing the beta-naphthylamides of Gly-Arg, Lys-Ala, Arg-Arg and Gly-Pro, respectively, were distinguished in homogenates of human muscle. Dipeptidyl peptidase I showed maximum activity at pH 5.0-6.0. Dipeptidyl peptidase II was maximally active at pH 5.0 and inhibited by cations. Dipeptidyl peptidases III and IV were most active at pH 8.5 and 7.5, respectively. When compared to controls, significant increases in muscle dipeptidyl peptidases I and II were observed in patients with muscular dystrophies and polymyositis. Dipeptidyl peptidase III was not altered in the neuromuscular disease examined. Dipeptidyl peptidase IV showed marked increase in a variety of muscle wasting conditions. The increase in dipeptidyl peptidases I and II may be attributed to lysosomal activation that is known to occur in conditions of muscle degeneration. However, the striking increase in a variety of muscle diseases of dipeptidyl peptidase IV, an enzyme shown to be associated with microsomal membranes in other tissues, suggest that in addition to lysosomes other sources also contribute to the total hydrolytic potential of diseased muscles. Dipeptidyl peptidases II and IV were found to be present in human serum. Their levels were not altered in serum of patients with Duchenne dystrophy.

Early elevation of cathepsin B1 in human muscle disease

Abstract Cathepsin B1 activity was determined in skeletal muscle of control subjects and of patients with major forms of muscular dystrophies, polymyositis, and certain denervating diseases. Cathepsin B1 activity was markedly increased in all diseases examined. This enzyme may thus play an important role in various muscle-wasting conditions in humans and, in fact, it may function as at least one rate-limiting enzyme of proteolysis in diseased muscle.

Distribution of acid hydrolases in guinea pig skeletal muscle.

Abstract The activity of five acid hydrolases was determined in the homogenates of skeletal muscle consisting of predominantly fast-twitch red, fast-twitch white or slow-twitch intermediate fibers in normal guinea pigs. The specific activities of arylsulfatase A, β-acetylglucosaminidase, β-galactosidase, acid cathepsin and acid phosphatase were found to be highest in the slow-twitch intermediate, medium in the fast-twitch red and lowest in the fast-twitch white fibers. These data provide additional biochemical characteristics of the various types of fibers which constitute guinea pig skeletal muscle.

Alkaline Phosphatase in Normal and Diseased Human Muscle

Summary The activity of alkaline phosphatase in skeletal muscle from normal persons and from patients with various myopathies and neuropathies was determined by a quantitative technique. Increased enzyme activity was found only in the severely abnormal muscles in patients affected with diseases of various etiologic origin. The results of this study confirm the original reported histo-chemical findings about this enzyme and suggest that the increased activity of alkaline phosphatase in diseased muscles is secondary to the pathologic changes. It may also be involved in some fashion in the process of muscle destruction.

NADP-linked dehydrogenases in duchenne muscular dystrophy

Abstract The activities of malic enzyme, glucose 6-phosphate dehydrogenase and isocitrate dehydrogenase were studied in muscles from patients with muscular dystrophies and other myopathies and neuropathies. The activities of all three NADP-linked enzymes were significantly higher in patients with Duchenne muscular dystrophy than in the controls. The results were discussed in relation to fat accumulation in muscle in Duchenne dystrophy.