Enzyme Activity In Skeletal Muscle Research Articles

Activity of antioxidant enzymes in rat skeletal muscle and brown fat: effect of cold and propranolol

1. Effects of acute (6 h) and chronic (21 day) cold (6°C) exposure, as well as propranolol (15 mg/kg) on the activities of CuZnSOD, MnSOD and catalase in the rat skeletal muscle (SM) and brown adipose tissue (BAT), which are important sites of cold-induced thermogenesis, were investigated. 2. The changes in the activity of antioxidant enzymes were tissue specific and dependent on the duration of cold exposure. Thus, in the SM of acutely cold exposed rats, the activity of all antioxidant enzymes studied was elevated, whereas in the BAT the activity of both SOD s decreased and that of catalase remained unchanged. In cold acclimated rats, the activity of all the three enzymes was increased in the BAT whereas in the SM, CuZnSOD activity was enhanced, MnSOD activity decreased and catalase activity returned to the control level. 3. Propranolol also differently altered the antioxidant enzyme activity in SM and BAT, alterations being dependent on the acclimation temperature. Thus, in room acclimated rats propranolol decreased the activity of all antioxidant enzymes in SM but did not affect those in BAT. However, in the SM propranolol prevented the elevation of MnSOD and catalase activities, induced by acute cold. In cold acclimated rats propranolol inhibited CuZnSOD activity in both SM and BAT but increased that of MnSOD.

EFFECT OF TREADMILL TRAINING AND CLENBUTEROL TREATMENT ON BODY FAT ACCUMULATION AND MUSCLE ENZYME ACTIVITIES OF RATS.

1392 The effects of exercise training, chronic administration of clenbuterol(β&2-adrenergic agonist), and the combination of these two treatment on body fat content and muscle enzyme activities were investigated. Forty male Sprague-Dawley rats were randomly assigned to one of four treatment groups: sedentary control(CON), clenbuterol(CL), exercise trained(TR), or exercise trained/clenbuterol(TR+CL). The training protocol consisted of running on motor-driven treadmill up an 8% grade, 5 days/wk for 8 weeks. Rats receiving clenbuterol were intubated with 0.8 mg/kg body wt/day dissolved in deionized water. Exercise training and clenbuterol administration significantly not only reduced the body fat content as evidenced by the decreasing retroperitoneal fat weight, but also increased the skeletal muscle mass without the changes of growth rate. The combined effect of these two treatment in increasing the muscle mass was additive, but in reducing the fat content, it was not additive. Chronic clenbuterol treatment significantly reduced the hexokinase and citrate synthase activities in skeletal muscle. These decreased enzyme activities significantly reduced endurance performance. Thus, the results of the current study indicate that the effects of clenbuterol treatment are the same as the effects of exercise training in body composition, but each of clenbuterol treatment and training inversely affects the changes in skeletal muscle enzyme activities of normal rats. Supported by Korea Research Foundation.

Reductions in type 1 fibre proportions and oxidative enzyme activity in skeletal muscle exist pre & post lung transplantation

Reductions in type 1 fibre proportions and oxidative enzyme activity in skeletal muscle exist pre & post lung transplantation

Skeletal Muscle Angiotensin-Converting Enzyme and its Relationship to Blood Pressure in Primary Hypertension and Healthy Elderly Men

The aim of this study was to investigate the relationships between angiotensin-converting enzyme (ACE) activity in serum and skeletal muscle to blood pressure and the long-term antihypertensive effects of fosinopril and atenolol. We examined 50 hypertensive patients randomized to receive 20 mg fosinopril or 50 mg atenolol daily for 16 weeks. ACE activity was measured in biopsy specimens from skeletal muscle. Measurements of office and ambulatory blood pressure, serum ACE, and left ventricular wall thickness were also performed. The same investigations were performed in a cross-sectional study of 50 healthy elderly men. Muscle ACE correlated inversely to blood pressure in cross-sectional analyses in both populations (p < 0.05). During atenolol treatment muscle ACE activity tended to increase (14%, p = 0.059), and this increase correlated inversely to the changes in standing systolic and diastolic blood pressure (r

Fiber type and citrate synthase activity in the human gastrocnemius and vastus lateralis with aging.

The purpose of this study was to determine whether enzymatic and histochemical characteristics of human skeletal muscle are altered with aging. Tissues from the vastus lateralis (VL) and gastrocnemius were analyzed for citrate synthase (CS) activity and fiber type in 55 sedentary men (age range 18-80 yr). In this population, CS activity in the gastrocnemius was negatively related to age (r = -0. 32, P < 0.05); there was no relationship in the VL. Treadmill-determined maximal oxygen consumption was positively related (r = 0.40, P < 0.05) to CS in the gastrocnemius but not in the VL. CS activity in the gastrocnemius was 24% lower in the oldest (>/=60 yr, n = 10) vs. the youngest (</=30 yr; n = 12) men; there was no change in CS activity in the VL with aging. No changes in fiber type were evident with age in either muscle. These data suggest a reduction in oxidative enzyme activity in human skeletal muscle with the aging process; this relationship may be muscle-group specific.

Genetic and other determinants of AMP deaminase activity in healthy adult skeletal muscle.

AMPD1 genotype, relative fiber type composition, training status, and gender were evaluated as contributing factors to the reported variation in AMP deaminase enzyme activity in healthy skeletal muscle. Multifactorial correlative analyses demonstrate that AMPD1 genotype has the greatest effect on enzyme activity. An AMPD1 mutant allele frequency of 13.7 and a 1.7% incidence of enzyme deficiency was found across 175 healthy subjects. Homozygotes for the AMPD1 normal allele have high enzyme activities, and heterozygotes display intermediate activities. When examined according to genotype, other factors were found to affect variability as follows: AMP deaminase activity in homozygotes for the normal allele exhibits a negative correlation with the relative percentage of type I fibers and training status. Conversely, residual AMP deaminase activity in homozygotes for the mutant allele displays a positive correlation with the relative percentage of type I fibers. Opposing correlations in different homozygous AMPD1 genotypes are likely due to relative fiber-type differences in the expression of AMPD1 and AMPD3 isoforms. Gender also contributes to variation in total skeletal muscle AMP deaminase activity, with normal homozygous and heterozygous women showing only 85-88% of the levels observed in genotype-matched men.

Lipid composition and lipolytic enzyme activities in porcine skeletal muscles with different oxidative pattern

Three muscles with different oxidative pattern ( m. longissimus dorsi, Ld; m. biceps femoris, Bf; m. triceps brachii, Tb) have been analysed for lipid composition and lipolytic activities. The results showed a relatively low lipid (around 30 g kg −1) and cholesterol (around 0.5 g kg −1) content being higher in the oxidative and intermediate muscles Tb and Bf, respectively, than in Ld. Muscle Tb had higher amount of phospholipids and PUFA. Muscle Tb also had the higher lipolytic activity (acid and neutral lipase and acid phospholipase activities). There were no differences for acid and neutral esterase activities between the three muscles studied. The use of principal component (PC) analysis might be used to distinguish among the three studied muscles since each one showed a different pattern based on the lipid composition and lipolytic activities.

Associations between skeletal muscle properties, physical fitness, physical activity and coronary heart disease risk factors in men

High physical fitness and physical activity are associated with favourable lipid levels, especially a high level of high density lipoprotein cholesterol (HDL-C). A person's skeletal muscle properties, metabolism and percentage of different muscle fibres (ST-%), which may modify coronary heart disease (CHD) risk factors, such as serum insulin, obesity and serum sex hormones may also influence his fitness level and leisure-time physical activity. We studied the associations of physical fitness, physical activity and ST-% with serum lipids and lipoproteins in 72 healthy men. Their parameters were compared with those of 20 men with defined CHD. Significant interrelationships between ST-%, fitness and leisure-time physical activity index (LTPAI) were observed. Multiple regression analysis showed that ST-%, fitness and leisure-time physical activity explained about 32% of the variation in HDL-C in the healthy men. In healthy men ST-% correlated positively with fitness ( r s=0.62, P<0.001) and with LTPAI ( r s=0.62, P<0.001). Fitness level also correlated significantly with LTPAI ( r s=0.81, P<0.001). Serum insulin showed negative associations with ST-% ( r s=−0.63, P<0.001) and fitness ( r s=−0.54, P<0.001) and LTPAI ( r s=−0.62, P<0.001). Free fraction of testosterone correlated negatively with serum HDL-C level ( r s=−0.34, P<0.01), with fitness ( r s=−0.41, P<0.001) and with LTPAI ( r s=−0.54, P<0.001). In sedentary men with the lowest fitness and physical activity the mean of ST-% (45%) was similar to that in CHD patients (44%). However, ST-% in men in the highest tertile of physical activity and fitness (68%) was significantly higher than in CHD patients and in men in the lowest tertile of physical activity and fitness. Skeletal muscle enzyme activity in lipid metabolism was significantly lower in both CHD patients and in sedentary and low-fit men than that in fitter and physically active men. The present data imply that skeletal muscle properties are important determinants of risk profiles, such as physical activity, fitness and serum lipid and lipoprotein patterns. Although fitness is a graded, independent predictor of mortality from CHD, a relatively high fitness level is not enough. This was clearly observed in the clustering analysis, in which the healthy men, according to their ST-%, fitness, leisure-time physical activity and serum sex hormone binding globulin (SHBG), fell into three natural groups: (i) Inactive men with lowest ST-% (mean 42%), lowest fitness (10.7 METs) and lowest HDL-C (1.36 mm/l); (ii) Fit men with high ST-% (66%), high fitness (14.5 METs) and moderately high HDL-C (1.54 mol/l); (iii) Active men with high ST-% (66%), highest fitness (14.9 METs) and highest serum HDL (1.83 mmol/l). The results support the idea that both fitness and physical activity give further protection against CHD by modifying risk factors. Our findings also suggest that skeletal muscle properties should be considered in the studies which assess CHD risk factors and their modifications especially in the field of health-related fitness.

Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure.

One of the primary consequences of left ventricular dysfunction (LVD) after myocardial infarction is a decrement in exercise capacity. Several factors have been hypothesized to account for this decrement, including alterations in skeletal muscle metabolism and aerobic capacity. The purpose of this study was to determine whether LVD-induced alterations in skeletal muscle enzyme activities, fiber composition, and fiber size are 1) generalized in muscles or specific to muscles composed primarily of a given fiber type and 2) related to the severity of the LVD. Female Wistar rats were divided into three groups: sham-operated controls (n = 13) and rats with moderate (n = 10) and severe (n = 7) LVD. LVD was surgically induced by ligating the left main coronary artery and resulted in elevations (P < 0.05) in left ventricular end-diastolic pressure (sham, 5 +/- 1 mmHg; moderate LVD, 11 +/- 1 mmHg; severe LVD, 25 +/- 1 mmHg). Moderate LVD decreased the activities of phosphofructokinase (PFK) and citrate synthase in one muscle composed of type IIB fibers but did not modify fiber composition or size of any muscle studied. However, severe LVD diminished the activity of enzymes involved in terminal and beta-oxidation in muscles composed primarily of type I fibers, type IIA fibers, and type IIB fibers. In addition, severe LVD induced a reduction in the activity of PFK in type IIB muscle, a 10% reduction in the percentage of type IID/X fibers, and a corresponding increase in the portion of type IIB fibers. Atrophy of type I fibers, type IIA fibers, and/or type IIB fibers occurred in soleus and plantaris muscles of rats with severe LVD. These data indicate that rats with severe LVD after myocardial infarction exhibit 1) decrements in mitochondrial enzyme activities independent of muscle fiber composition, 2) a reduction in PFK activity in type IIB muscle, 3) transformation of type IID/X to type IIB fibers, and 4) atrophy of type I, IIA, and IIB fibers.

Energy expenditure using isotope-labelled water (2H218O), exercise performance, skeletal muscle enzyme activities and plasma biochemical parameters in humans during 95 days of endurance exercise with inadequate energy intake.

Two men, R.F. and M.S., pulled sledges each with starting masses of 222 kg, 2300 km across Antarctica. Exercise was performed for approximately 10 h each day for 95 days. Despite an average energy intake of 21.3 MJ.day-1 both subjects lost more than 25% of body weight. Energy expenditure was measured using energy balance data (EB) and isotope-labelled water (2H218O). Isotope doses were taken on day 0 and day 50 of the expedition. During the first 50 days both methods gave reasonable agreement, giving energy expenditures of 38.3 (EB) and 35.5 (2H218O) MJ.day-1 in R.F. and 28.6 (EB) and 29.1 (2H218O) MJ.day-1 in M.S. The isotope data for days 20-30 yielded exceptional values of 44.6 MJ.day-1 in R.F. and 48.7 MJ.day-1 in M.S. Estimates of energy expenditure between day 51 and day 96 were much lower and although the methods were in agreement for R.F.-24.1 (EB) and 23.1 (2H218O) MJ. day-1, there was poor agreement for MS-26.8 (EB) and 18.8 (2H218O) MJ.day-1. However, some practical difficulties occurred during this second period and there were also problems arising from marked increases in body water that made estimates of body mass and composition change difficult to interpret. The latter problems were probably due to malnutrition, which may have also been responsible for surprising increases in urinary excretion of 2H and 18O observed in both men at around day 81. These increases may reflect the release of label incorporated into molecules other than water which do not normally freely exchange with the body water pool under the circumstances of marked malnourishment. Following the expedition, both men showed declines in maximal O2 consumption (VO2max, 53.6 to 41.2 ml O2 kg-1.min-1 in R.F., 58.1-46.0 ml O2 kg-1.min-1 in M.S.); maximal voluntary isometric force production in different muscle groups (up to 19.9% in R.F. and 55.8% in M.S.) and both cytoplasmic and mitochondrial skeletal muscle enzyme activities (up to 56% in R.F. and 63% in M.S.). Plasma samples taken during the expedition showed low glucose levels, inappropriately high insulin levels, and declines in testosterone and luteinizing hormone. Thyroxine, cholesterol, albumin and triglyceride levels remained normal.

Changes in skeletal muscle morphology and biochemistry after cardiac transplantation

Skeletal muscle biopsies (vastus lateralis) were performed in 12 patients (mean age 47 ± 11 years) before and at 3 and 12 months after cardiac transplantation. Fiber type analysis revealed a predominance of type II fibers before cardiac transplantation (66 ± 10%); the ratio did not change after transplantation. Fiber crosssectional area increased by 35% to 39% in all fiber types by 12 months after cardiac transplantation. Fiber crosssectional area, however, remained below the reported normal values. The number of capillaries surrounding each fiber did not change after cardiac transplantation. Skeletal muscle enzyme activity of phosphofructokinase, citrate synthase, and β-hydroxyacyl coenzyme A dehydrogenase increased by 26%, 47%, and 63%, respectively, after cardiac transplantation (p < 0.05). Peak oxygen uptake also increased significantly after cardiac transplantation (19.5 ± 8.1 ml/kg/min at 12 months vs 9.8 ± 1.4 ml/kg/min before transplant, p < 0.01); however, uptake remained 40% below that of predicted. Thus, significant improvement in skeletal muscle morphology and biochemistry occurs in the first year after cardiac transplantation in association with improved exercise capacity. Recovery, however, may be incomplete, which could explain residual impairment of exercise capacity in these patients.

Skeletal muscle characteristics and metabolic response to exercise in young Standardbreds

Abstract Objective To determine whether performance capacity in a group of young trained Standardbreds is related to skeletal muscle characteristics and metabolic response to exercise. Animals 13 clinically normal 2-year-old Standardbreds. Procedure Venous blood and middle gluteal muscle biopsy samples were obtained from each horse within 1 to 2 minutes after trotting at high speed for 1,600 m. Results There was a positive correlation between plasma lactate and muscle glucose-6-phosphate (G-6-P) concentrations and trotting speed. There was a negative correlation between muscle adenosine triphosphate concentration and trotting speed, plasma lactate concentration, and muscle lactate and G-6-P concentrations. Muscle concentration of G-6-P was positively correlated with muscle lactate and plasma lactate concentrations. Percentage of type-1, -2A, and -2B fibers in skeletal muscle and muscle enzyme activities of hexokinase, 3-OH-acyl-CoA dehydrogenase, lactate dehydrogenase, and citrate synthase were not correlated with trotting speed. Conclusion Speed of trotting at a distance of 1,600 m in young trained Standardbreds is related to the ability of muscle to produce energy by use of anaerobic glycolysis. (Am J Vet Res 1997;58:167–170)

Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists.

Skeletal muscle buffering capacity (beta m), enzyme activities and exercise performance were measured before and after 4 weeks of high-intensity, submaximal interval training (HIT) undertaken by six well-trained competitive cyclists [mean maximal oxygen consumption (VO2max) = 66.2 ml.kg-1.min-1]. HIT replaced a portion of habitual endurance training and consisted of six sessions, each of six to eight repetitions of 5 min duration at 80% of peak sustained power output (PPO) separated by 1 min of recovery. beta m increased from 206.6 (17.9) to 240.4 (34.1) mumol H+.g muscle dw-1.pH-1 after HIT (P = 0.05). PPO, time to fatigue at 150% PPO (TF150) and 40-km cycle time trial performance (TT40) all significantly improved after HIT (P < 0.05). In contrast, there was no change in the activity of either phosphofructokinase or citrate synthase. In addition, beta m correlated significantly with TT40 performance before HIT (r = -0.82, P < 0.05) and the relationship between change in beta m and change in TT40 was close to significance (r = -0.74). beta m did not correlate with TF150. These results indicate that beta m may be an important determinant of relatively short-duration (< 60 min) endurance cycling activity and responds positively to just six sessions of high-intensity, submaximal interval training.

SEVERE MYOCARDIAL INFARCTION DIMINISHES AEROBIC CAPACITY OF RAT SKELETAL MUSCLE 364

Studies of heart failure in humans and rats have demonstrated that alterations in skeletal muscle metabolism and aerobic capacity occur. The purpose of this study was to determine whether myocardial infarction-induced alterations in skeletal muscle enzyme activities are generalized in muscles or are specific to muscles composed primarily of a given fiber type. The activity of several enzymes involved in glycolysis (phosphofructokinase [PFK] and lactate dehydrogenase [LDH]), terminal oxidation (citrate synthase [CS] and malate dehydrogenase [MDH]) and β-oxidation of fatty acids (3-hydroxyacyl CoA dehydrogenase [HADH]) were measured in soleus (S; type I fibers), plantaris (P; mixed fiber type), and the deep red (GR; type I and IIA fibers), middle (GM; mixed fiber type) and superficial white(GW; type IIB fibers) portions of gastrocnemius muscles from female Wistar rats. The animals were divided into three groups: shamoperated controls(n=13) and rats with moderate (45 ± 2%; n=10) and large (59 ± 4%; n=7) myocardial infarcts (MI). MI were surgically induced by ligating the left main coronary artery and after 2 months resulted in increases (P<0.05) in left ventricular end diastolic pressure (sham 5 ± 1 mmHg; moderate MI 11 ± 1; large MI 25 ± 1). Neither PFK nor LDH was different in either MI group compared to controls. Additionally, moderately sized MI induced little change in any of the enzyme activities. However, in rats with large MI, CS was lower in S (sham 24 ± 1μmol·min-1·g wet wt-1; large MI 18 ± 1), GR (sham 37 ± 2; large MI 31 ± 1) and GW (sham 8± 2; large MI 6 ± 1); MDH was lower in GR (sham 779± 2 μmol·min-1·g wet wt-1; large MI 656± 37) and GW (sham 210 ± 2; large MI 171 ± 4); and HADH was lower in P (sham 12 ± 1 μmol·min-1·g wet wt-1; large MI 9 ± 1) and GR (sham 17 ± 1; large MI 12 ± 1). These data indicate that reductions in aerobic capacity associated with heart failure occur in skeletal muscle regardless of fiber composition, and changes in enzyme activities appear to occur when severe heart failure is present.

RELATIONSHIPS OF OBESITY AND FITNESS TO MUSCLE METABOLIC PROFILE902

Skeletal muscle fiber type and enzyme activities have been linked to insulin resistant states such as Type II diabetes, hypertension, and obesity. But these conditions are associated with and confounded by low aerobic fitness. To determine the independent relationships of obesity and fitness to muscle fiber type and metabolic profile, we matched lean (L) and obese (O) men(n=49) at 2 levels of fitness: low (LF) with VO2 max <3.2 L/min, and high (HF), VO2 >3.2 L/min, in a 2×2 design. All groups were matched on fat-free mass and at each level of obesity, LF and HF were matched on% fat (16±1 vs 33±2%). Muscle biopsy samples from the vastus lateralis were analyzed for enzyme activities (U/g wet weight) and fiber type.Table Obesity and low fitness were independently associated with an increased% Type IIB and reduced% Type I fibers, with no interaction. Obesity was associated with significantly increased phosphofructokinase (PFK) activity, whereas the citrate synthase (CS) activity was increased in both HF groups, independent of obesity (P<0.05). The PFK/CS ratio, an index of the glycolytic/aerobic-oxidative potential of muscle, was significantly increased both by low fitness and obesity (P<0.01). Thus, obesity and fitness both independently impact on muscle fiber type and metabolic potential. These results indicate that fitness may offset but not completely compensate for some of the metabolic correlates in muscle of increased body fat which tend to favor carbohydrate over fat oxidation and may predispose to the onset or persistence of the obese state.

Effect of endurance training under hypoxic condition on oxidative enzyme activity in rat skeletal muscle.

The adaptive response of oxidative enzyme activity in the skeletal muscle to training in normoxic and in normobaric hypoxic training was studied. Forty male Wistar rats were divided into 4 groups: normoxia + sedentary (NS, n = 10); hypoxia + sedentary (HS, n = 10); normoxia + training (NT, n = 10); and hypoxia + training (HT, n = 10). Rats in the NT group ran on a treadmill for 30 min a day at 20-30 m.min-1, 4 days a week for 10 weeks in normoxia. Rats in the HT group performed the same training protocol as NT in an ambient FIO2 decreased to 12%. HS rats were exposed to hypoxia in the same degree, duration and frequency as HT without exercise. After the training period, the soleus and the plantaris muscles were removed, and the activities of mitochondrial enzymes, malate dehydrogenase (MDH) and 3-hydroxyacyl-CoA dehydrogenase (HAD) were measured by a spectrophotometer. The normoxic training did not increase MDH or HAD activities, in either the soleus or the plantaris. This absence of change in mitochondrial enzyme activities is considered to be the results of inadequate stimulus of training, including a relatively low amount of exercise. On the other hand, the hypoxic training enhanced the MDH activity in the soleus by 17.5% compared with NS (P < 0.01) and by 20.5% compared with HS (P < 0.01). Also in the plantaris, the MDH activity in HT was higher than that in HS (15.7%, P < 0.05). These findings suggest that even moderate training by which enzyme activity is not increased under normoxic conditions can enhance the oxidative capacity in the skeletal muscle when the training is performed in a hypoxic environment.

The Comparison of Oxidative Enzyme Activity in Skeletal Muscle from Stroke-Prone Spontaneously Hypertensive and Normotensive Rats

The Comparison of Oxidative Enzyme Activity in Skeletal Muscle from Stroke-Prone Spontaneously Hypertensive and Normotensive Rats

Effects of hypoxia on enzyme activities in skeletal muscle of rats of different ages. An attempt at pharmacological treatment

The activities of enzymes related to energy metabolism in the gastrocnemius and soleus muscles in young-adult (4 months), mature (12 months) and senescent (24 months) rats were compared after 72 h of continuous exposure to normobaric hypoxia or normoxia after alpha-adrenergic antagonist nicergoline or saline solution had been given intraperitoneally for 30 consecutive days. The maximum rates (Vmax) of the following enzyme activities in the crude extract and/or the mitochondrial fraction of each muscle specimen were evaluated: (1) for the anaerobic glycolytic pathway: hexokinase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase; (2) for the tricarboxylic acid cycle; citrate synthase and malate dehydrogenase; (3) for the electron transfer chain; cytochrome oxidase; and (4) for the NAD+/NADH redox state: total NADH cytochrome c reductase. The significant differences between the enzyme activities at different ages or under different experimental conditions in the two tissue preparations of the two muscles were determined by ANOVA. MCA and ETA were used to evaluate the net effects of the experimental conditions. Ageing did not seem to affect the soleus and gastrocnemius muscles in the same way. Changes were seen only in the glycolytic pathway enzymes in the crude extract from the gastrocnemius muscle. In the soleus muscle changes in enzyme activities as a function of ageing were also found in the mitochondrial fraction. We also found that hypoxia caused greater changes in 12-month-old rats than in those of other ages (especially in the enzyme activities of the gastrocnemius muscle). Finally out data show that only in certain cases was the pharmacological treatment able to modify the influence of hypoxic conditions on the levels of enzyme activities, regardless of the age of animals.

Lysosomal enzyme activities in skeletal muscle of patients with neuromuscular diseases

Activities of nine lysosomal enzymes and pH-dependent isozyme patterns of alpha-mannosidase were examined in the skeletal muscle of patients with neuromuscular diseases, and the ratios of these enzyme activities in leukocytes to those in myocytes (L/M ratio) were determined. The activities of enzymes with a high L/M ratio were markedly increased in the muscles of patients with Duchenne muscular dystrophy (DMD), myotonic dystrophy (MyD), or polymyositis (PM). In contrast, those which showed a low L/M ratio were increased in the muscles of amyotrophic lateral sclerosis (ALS) and disuse muscle atrophy (DUA). The isozyme pattern of alpha-mannosidase in DMD muscle resembled that in leukocytes, while those in ALS and DUA muscle resembled that in normal muscle. These results may suggest that the increased activity of lysosomal enzymes in the muscles of patients with DMD, MyD, or PM is due primarily to infiltrating leukocytes, while that in patients with ALS or DUA is due to intramyofiber lysosomes.

Correlation Between Mitochondrial DNA 4977-bp Deletion and Respiratory Chain Enzyme Activities in Aging Human Skeletal Muscles

The content of the mitochondrial DNA 4977-bp deletion and the respiratory chain enzyme activities were determined in the same human skeletal muscle specimens. A direct correlation between damage to mtDNA and bioenergetic deficiency was observed. The time-course of the appearance of the mtDNA deletion was followed. The highest percentage of mtDNA-deleted molecules was 0.26% and it was found in the eighties which corresponds to the age of the major reduction in the respiratory chain enzyme activities. Two samples with very low mitochondrial respiratory enzyme activities exhibited much higher levels of deletion compared to the similar age counterparts. Given, however, the low absolute level of the deletion also in these samples, we suggest that damage to the respiratory chain complexes, especially complex IV, might be the cause more than the effect of the increased number of mtDNA molecules bearing deletions in aged human skeletal muscle.