Molecular interaction of the proteasome (multicatalytic proteinase). Evidence that the proteasome is not a constituent of the '26 S' multienzyme complex

On the basis of recent reports that suggested that proteasomes, via an ATP-dependent process, become integral components of a '26 S' complex possessing 3-carboxypropionyl-Leu-Leu-Val-Tyr 4-methylcoumarin-7-ylamide-hydrolysing activity, we have investigated the molecular interaction of proteasomes in ATP-stabilized fraction II (proteins absorbed on DEAE-matrix and eluted with 0.5 M-KCl) of rabbit reticulocytes and mouse liver. Analysis of the various extracts by (NH4)2SO4 fractionation, velocity-gradient centrifugation, non-denaturing PAGE and SDS/PAGE and immunoblotting with proteasome-specific antisera failed to identify the proteasome as part of a higher-molecular-mass '26 S' multienzyme complex. In all instances proteasomes are identified in their 'free' 650 kDa '20 S' form. In addition to the proteasome and independent of the presence of MgATP, we isolated a high-molecular-mass proteinase whose electrophoretic migration behaviour and sedimentation rate correspond to that of the previously described '26 S' proteinase. This '26 S' proteinase possesses a strong 3-carboxypropionyl-Leu-Leu-Val-Tyr 4-methylcoumarin-7-ylamide-hydrolysing activity and is composed of several non-identical polypeptides in the molecular-mass range 20-150 kDa. Despite its similarity to proteasomal enzyme activity, protein analysis and immunoblotting experiments demonstrate that neither the intact proteasome nor subunits thereof are components of the '26 S' proteinase complex.

Localization of subunits in proteasomes from Thermoplasma acidophilum by immunoelectron microscopy

The subunit topography of the Thermoplasma acidophilum proteasome was determined by immunoelectron microscopy using monospecific antibodies directed against the two constituent subunits (alpha,beta). Anti-alpha-subunit IgG was found to bind to the outer disks of the cylinder- or barrel-shaped molecule, while the binding sites of the anti-beta-subunit IgG were mapped on the two inner rings. Probably the homologues of the two subunits in the compositionally more complex but isomorphous eukaryotic proteasomes occupy equivalent positions.

The three-dimensional structure of proteasomes from Thermoplasma acidophilum as determined by electron microscopy using random conical tilting

The three-dimensional structure of proteasomes from the archaebacterium Thermoplasma acidophilum has been determined to a resolution of approximately 2 nm from electron micrographs of negatively stained preparations using the method of 'random conical tilting'. The particles turn out to be essentially cylinder-shaped barrels, 15 nm long and 11 nm wide, enclosing a tripartite inner compartiment. An account is given of some of the present limitations which prevent to attain a higher resolution and possible ways to overcome these limitations are indicated.

Cloning and sequencing of the gene encoding the large (alpha-) subunit of the proteasome from Thermoplasma acidophilum

The gene encoding the alpha-subunit of the proteasome from the archaebacterium Thermoplasma acidophilum was cloned and sequenced. The gene encodes for a polypeptide with 233 amino acid residues and a calculated molecular weight of 25870. Sequence similarity of the alpha-subunit with the Saccharomyces cerevisiae wild-type suppressor gene scll+ encoded polypeptide, which is probably identical with the subunit YC7-alpha of the yeast proteasome, lends support to a putative role of proteasomes in the regulation of gene expression. The significant sequence similarity to the various subunits of eukaryotic proteasomes make it likely that proteasomal proteins are encoded by one gene family of ancient origin.

Effect of the multicatalytic proteinase (prosome) on translational activity in rabbit reticulocyte lysates

In a message-dependent reticulocyte lysate translation system, incorporation of [3H]leucine into acid-insoluble protein is increased following selective removal of the multicatalytic proteinase (MCP) with a monospecific antibody. Re-addition of active proteinase to previously depleted lysates reverses this effect in that the same low levels of translational product are measured as in untreated lysates. Addition of histone-stimulated MCP further depresses the level of protein product. Conversely, lysates supplemented with inactivated MCP retain the higher level of translational activity which is measured after precipitation of the enzyme with antibody. In these lysates, the effect of the antibody on translational activity is inversely correlated with that on hydrolytic activity towards [14C]methylcasein or N-succinyl-Leu-Leu-Val-Tyr-4-methyl-7-coumarylamide, two substrates of the MCP. These results showing that the MCP is capable of modulating translational activity in vitro, suggest an important role of this molecule in the in vivo translational process.

Extracellular matrix changes following blunt trauma to rat skeletal muscles

Myofiber injury-repair was studied in the rat following blunt trauma to the lower leg in order to understand how the inflammatory and regenerative responses of muscles are altered when myofiber rupture is accompanied by bleeding and clotting reactions. A contusion injury to the muscles of the lower hindlimb of the rat was induced by applying an impact force of 4.7 N-m/cm2 to one leg. The gastrocnemius and soleus muscles were removed bilaterally and evaluated by histochemical and immunohistochemical techniques to document myofiber, vascular, and connective tissue alterations for several days following insult (6-120 hr). A significant increase in wet weight of the gastrocnemius muscle was noted 24 hr postinjury as fluid accumulation and bruising were evident in the muscles resulting from bleeding and inflammation. Vascular disruption was confirmed by the localization of some plasma constituents (fibrinogen, albumin, and complement C3) throughout the interstitial space and even inside some of the damaged myofibers. Inflammation was present and persisted for 5 days as evidenced by continued mast cell degranulation and increased vascular permeability. Using antibodies to identify specific proteoglycans which appear or disappear at various times during muscle regeneration, muscle repair could be followed. The repair process required approximately 10 days for restoration of morphologically intact myofibers. Thus, myofiber repair processes appear to be maintained even after disruption of the vascular system and ischemia following blunt trauma.

The multicatalytic proteinase (prosome) is ubiquitous from eukaryotes to archaebacteria

From the thermoacidophilic archaebacterium, Thermoplasma acidophilum, a proteolytically active particle has been isolated which is almost identical in size and shape with the multicatalytic proteinase (prosome) from rat. This result indicates that prosomes have been developed early in evolution and that they possibly serve functions common to all living cells.

ATP-activated, high-molecular-mass proteinase-I from rat skeletal muscle is a cysteine proteinase-alpha 1-macroglobulin complex

From rat skeletal muscle tissue we have isolated and purified a proteolytic activity of molecular mass 750 kDa. The enzyme, designated 'proteinase I', which has been found to be located in capillaries of skeletal muscle tissue, catalyzes the hydrolysis of Z-Phe-Arg-MCA and [14C]methylcasein and this process is activated about 2-fold by ATP. As judged by SDS-polyacrylamide gel electrophoresis the subunit pattern of 'proteinase I' is similar to alpha-macroglobulin. Immunoelectrophoretic analyses of 'proteinase I' with antisera to rat alpha 1-macroglobulin, alpha 2-macroglobulin, and rat liver cathepsins reveal that this high-molecular-mass proteinase is a complex of alpha 1-macroglobulin and the cysteine proteinases cathepsin B, H and L. A similar 'proteinase' has been isolated from rat serum. Two ATP-activated high molecular-mass proteinases that have been previously identified in liver and heart muscle by other investigators equally show a positive immunological reaction with the antiserum raised against 'proteinase I'. From these data, together with results presented in an accompanying paper (Kuehn, L., Dahlmann, B., Gauthier, F. and Neubauer, H.-P. (1989) Biochim. Biophys. Acta 991, 263), we conclude that the ATP-stimulated high-molecular-mass proteolytic activity is partly due to the presence of a complex of alpha-macroglobulin and cysteine proteinases.

High-molecular-mass proteinases in rabbit reticulocytes: the multicatalytic proteinase is an ATP-independent enzyme and ATP-activated proteolysis is in part associated with a cysteine proteinase complexed to alpha 1-macroglobulin

We have investigated the proteolytic degradation of [14C]methylcasein and 125I-labeled bovine serum albumin at pH 7.8 and 37 degrees C by lysates of rabbit reticulocytes purified from rabbit blood by two different procedures. (I) Lysates obtained from reticulocytes after removal of plasma and buffy coat as well as after washing of cells, degraded casein and albumin, and released from the two substrates 1.3%/h and 0.4%/h, respectively, of acid-soluble radioactivity. The activity towards both substrates was stimulated about 4-fold by ATP/Mg2+. Chromatography of whole blood on a column of cellulose prior to washing and lysis of cells had profound but differential effects on these activities in that stimulation of casein-degradation by ATP/Mg2+ was almost completely lost, whereas degradation of albumin, albeit at a low rate, was measurable in the presence of ATP/Mg2+ only. (II) Degradation of casein by these lysates is largely inhibited by a monospecific antibody against rabbit multicatalytic proteinase, whereas digestion of albumin is not affected by the antibody, either in the presence or absence of ATP/Mg2+. The latter activity is partially inhibited by a specific antibody against rabbit alpha 1-macroglobulin. (III) The immunoreactive amount of multicatalytic proteinase is about 1.2 micrograms per mg of lysate protein and almost identical in the two lysates. In contrast, the immunologically detectable levels of alpha 1-macroglobulin vary and are much lower in reticulocyte-lysates following chromatography on cellulose than in lysates from washed reticulocytes. (IV) Caseinolytic activity of multicatalytic proteinase, purified from rabbit reticulocyte lysate, is not activated by ATP/Mg2+ and the enzyme is proteolytically inactive towards albumin. On the other hand, a complex consisting of the proteinase inhibitor alpha 1-macroglobulin and the cysteine proteinase, cathepsin B, does degrade both substrates at pH 7.8, in an ATP/Mg2+-activated fashion. From these results it is concluded that the multicatalytic proteinase is an ATP-independent enzyme and a cellular constituent of rabbit reticulocytes whereas the activity stimulated by ATP/Mg2+ appears to be associated, at least in part, with a cysteine proteinase complexed to alpha 1-macroglobulin.

Electron microscopy and image analysis of the multicatalytic proteinase

One electron micrographs, negatively stained multicatalytic proteinase molecules are viewed end-on (ring shaped) or side-on (rectangular shaped). For aurothioglucose, ammonium molybdate- and phosphotungstate-stained molecules, the dimensions measured are consistent. In contrast, uranyl acetate-staining reveals ring-shaped particles which vary in diameter between 12 and 16 nm. This is due to a partial collapse and substantial flattening of the structure. Digital image analysis of side-on views of the particles reveals a tripartite, reel-shaped structure. Within the ring-like, end-on projections of ammonium molybdate-stained molecules six local centres of mass can be discerned; their position appears to depart, however, from a true six-fold symmetry.

Characterization of muscles injured by forced lengthening. I. Cellular infiltrates

Myofiber injury-repair was studied in rat soleus muscles to elucidate the role of infiltrating cells in the injury-repair process. Muscle injury was induced by forced muscle lengthening with the contralateral muscle serving as a control. The muscles were removed for histologic, histochemical and immunohistochemical procedures at varying periods (12-120 h) post-injury. All injured muscles were severely damaged with many cells present in the interstitial spaces between myofibers. Normal appearing myofibers demonstrated elevated lysosomal proteolytic activity, but no evidence of increased activity, indicative of phagocytic cells, was found in or between damaged myofibers. The esterase stain for macrophages and immunohistochemical techniques for mast cells also provided no support for either cell type predominating in the damaged area, although mast cell degranulation could be observed in the pericapillary regions. In contrast, the use of a specific antisera for a multicatalytic protease uniquely defined most of these cells as myogenic in origin. They appeared to be most numerous between the torn ends of a myofiber. Surprisingly, the remainder of the cells appeared to be of lymphoid origin.

Changes in proteinase/proteinase inhibitor levels in rat skeletal muscle tissue during diabetes and fasting

The skeletal muscle content of three rat proteinase inhibitors, a 1-proteinase inhibitor, contrapsin and a 1-cysteine proteinase inhibitor was measured by immunochemical techniques following streptozotocin-induced diabetes. When compared with normal rats, a 1-cysteine proteinase inhibitor and a 1-proteinase inhibitor levels remained essentially unchanged, whereas the content of rat contrapsin was reduced by nearly 80% after the onset of diabetes. Similarly, fasting of rats for three days resulted in a lowering of the levels of contrapsin in skeletal muscles. Under these conditions, levels of chymotrypsin-like activity (chymase) were increased by 150%, whereas the content of the trypsin-like, neutral proteinase was unchanged. Kinetic studies in vitro with Tosyl-Gly-Pro-Arg-4-nitroanilide as substrate showed no inhibition of the trypsin-like proteinase by a 1-proteinase inhibitor, while contrapsin inhibited the enzyme with a Ki value of 40nM. The changing pattern of these proteinases and their potential inhibitors (chymase/a 1-proteinase inhibitor and trypsin-like proteinase/contrapsin) may be a factor contributing to muscle wasting as observed in diabetes and fasting.

Drosophila small cytoplasmic 19S ribonucleoprotein is homologous to the rat multicatalytic proteinase

All eukaryotic cells so far analysed contain 19S particles which share a cylinder-like shape and are composed of a set of proteins of relative molecular mass ranging typically from 19,000 to 36,000 (refs 1-10). Proposed functions have included synthetase activity, transfer RNA processing or messenger RNA repression, but their biological importance remains obscure. A multicatalytic proteinase (MCP) of similar size and shape has been isolated from mammalian tissues. The apparent similarities of these high molecular weight complexes suggest a biochemical and functional homology between the small cytoplasmic 19S particle from Drosophila melanogaster (19S-scRNP) (ref. 7) and rat MCP (ref. 14). By means of electron microscopy, immunological techniques, RNA identification and proteinase activity assays, we were able to show that the two structurally similar complexes are immunologically related ribonucleoproteins (RNPs) with similar proteolytic activity.

Activity of a gelsolin-like actin modulator in rat skeletal muscle under protein catabolic conditions

A gelsolin-like actin-modulating protein was isolated from rat skeletal muscle and characterized with respect to its interaction with actin. The protein, with a molecular mass of approx. 85 kDa, forms a stoichiometric complex with two actin molecules and is activated by micromolar concentrations of Ca2+. It effectively severs actin filaments and promotes nucleation of actin polymerization. The activity of this protein is detectable already in crude extracts by its capability to reduce the steady state viscosity of actin. Actin-modulating activities were determined in muscle extracts of rats kept under protein catabolic conditions, i.e. as generated by corticosterone treatment and starvation. In both cases we found a marked increase of modulator activity. The possibility is discussed that the increased activity of actin modulator indicates a fragmentation of actin filaments prior to the proteolytic degradation of actin.

Localization of a multi-catalytic, high-molecular mass proteinase in the nuclei of muscle cells

A multi-catalytic protease in muscle cells was uniquely localized to the nucleus of muscle cells, both in cell culture and in sections of muscle tissue. Although no specific substructure of the nucleus could be identified as the site of the enzyme by immunocytochemical techniques, the enzyme was nevertheless present in all muscle cell nuclei. It appears that MCP is a useful marker for nuclei found specifically in muscle tissue.

Immunochemical characterisation of the myofibrillar proteinase from cultured rat myocytes as chymase

The proteinase extracted from the myofibrillar fraction of (a) primary rat myocytes and (b) the L-8 myogenic cell line, both maintained in culture, was identified by immunochemical analysis as chymase, the chymotrypsin-like serine proteinase of rat mast cells. Chymase would therefore appear to be an intrinsic protein in the rat myocyte also.

Alkaline proteinase localization in myoblasts

Recent interest in elucidating the role of non-lysosomal proteases in intracellular protein catabolism in muscle has led to various investigations with three alkaline proteases: a trypsin-like, a chymotrypsin-like, and a high molecular weight cysteine proteinase. Although in vitro biochemical assays have revealed the catabolic potential of at least two of these proteases, confirmation of their presence in muscle cells has been difficult. In this study immunohistochemical techniques were employed to localize each of these proteases in rat myoblasts. Antisera against the trypsin-like and chymotrypsin-like proteinase (both serine proteinases) showed strong localization in the cytoplasm immediately around the nucleus. Both also stained chromatin material in the nucleus of these cells. Fluorescent localization of the high molecular weight cysteine proteinase (Proteinase I) also appeared to be cell-associated in the myoblasts. The use of myoblasts in cell culture sections of whole muscle was advantageous, since localization of the proteases could be assessed in the absence of other cell types.

Size and shape of the multicatalytic proteinase from rat skeletal muscle

The multicatalytic proteinase from rat skeletal muscle, a non-lysosomal high molecular weight enzyme active at neutral to alkaline pH, has been examined in the electron microscope as well as by dynamic laser light scattering. Both methods reveal monodisperse particles. Electron micrographs show a cylinder-shaped complex with a diameter of 11 nm and a length of 16 nm in negatively stained, and a diameter of 9.6 nm and a length of 14.3 nm in freeze-dried, heavy metal replicated specimens. The molecule is composed of four rings or disks.

Effect of starvation or treatment with corticosterone on the amount of easily releasable myofilaments in rat skeletal muscles

Treatment of isolated myofibrils with an ATP-containing relaxing solution results in the dissociation of a preformed quantity of myofilaments called 'easily releasable myofilaments'. Van der Westhuyzen, Matsumoto & Etlinger [(1981) J. Biol. Chem. 256, 11791-11797] presented experimental evidence that these myofilaments represent intermediate products in the turnover of myofibrillar proteins. To investigate further this question, we measured the size of the fraction of easily releasable myofilaments in three different species of skeletal muscles from rats subjected to well-defined catabolic conditions, namely starvation or chronic glucocorticoid administration. The results were as follows: (1) The amount of easily releasable myofilaments was transiently increased about 2-3-fold during both experiments, and thus paralleled the known alterations in the rate of overall muscle protein breakdown rather than in those of synthesis. (2) These changes were observed in muscles containing predominantly fast-twitch fibres, but not in slow-twitch soleus muscle, a muscle that is known to be more resistant to catabolic conditions. (3) The starvation-induced increase of the size of the fraction of easily releasable myofilaments could be significantly reduced by treatment of the starving animals with the proteinase inhibitor E-64. These results are compatible with the idea that easily releasable myofilaments are intermediates in the degradative pathway of myofibrillar proteins and that a proteolytic step may be involved in the conversion of myofilaments into easily releasable myofilaments.

Fluorescence methods for localizing proteinases and proteinase inhibitors in skeletal muscle

Proteinases and proteinase inhibitors have become suspect in a wide variety of muscle wasting conditions that might be treatable if knowledge of the cellular locale and function of these molecules were known. Fluorescent probes have been useful in the localization of proteinases in muscle samples from human and animal specimens. These include the histochemical localization of proteinases based on the specific fluorescence of hydrolysis product derivatives, but this approach has been limited to the lysosomal proteinases because of the acidic requirements of the trapping reaction of the primary reaction product. Immunohistochemical techniques do not have the same restrictions and a number of lysosomal and nonlysosomal proteinases have been identified in muscle by this means. Unfortunately, they do not yield any information as to the activity of the enzymes. This is an important consideration since the extracellular environment contains a number of proteinase inhibitors, some of which may be internalized by the cell.

Activation of the multicatalytic proteinase from rat skeletal muscle by fatty acids or sodium dodecyl sulphate

A multicatalytic proteinase from rat skeletal muscle contains active site(s) catalysing the degradation of benzoyl-Val-Gly-Arg 4-methyl-7-coumarylamide, succinyl-Ala-Ala-Phe 4-methylcoumarylamide and [14C]methylcasein as well as benzyloxy-carbonyl-Leu-Leu-Glu 2-naphthylamide. These activities are 7-14-fold activated by 1 mM-sodium dodecyl sulphate. The activation leads to a higher susceptibility to the proteinase inhibitor chymostatin and to a lower ability to be inhibited and precipitated by antibodies raised against the non-activated enzyme. Since no changes in Mr or subunit composition were observed in the SDS-activated form, some conformational changes seem to occur during the activation step. More pronounced activation was observed in the presence of physiological concentrations of fatty acids; oleic acid at 100 microM concentrations stimulated the proteinase about 50-fold. In contrast with the non-activated proteinase, the activated enzyme considerably degrades muscle cytoplasmic proteins in vitro. Thus it is not unlikely that, in vivo, potential activators such as fatty acids can induce the multicatalytic proteinase to participate in muscle protein breakdown.

Purification and characterization of a multicatalytic high-molecular-mass proteinase from rat skeletal muscle

A proteolytic enzyme was purified from the post-myofibrillar fraction of rat skeletal muscle. The purification procedure consisted of fractionation of the muscle extract by (NH4)2SO4, chromatography on DEAE-Sephacel, fast protein liquid chromatography on Mono Q and gel filtration on Sepharose 6B. The enzyme preparation appeared to be homogeneous as judged by disc electrophoresis in polyacrylamide gels and by immunoelectrophoresis. The isoelectric point of the proteinase is at 5.1-5.2. The enzyme has an Mr of about 650 000 and dissociates into eight subunits of Mr 25 000-32 000 when subjected to electrophoresis in sodium dodecyl sulphate/polyacrylamide gels. The proteinase contains hydrolytic activity against N-blocked tripeptide 4-methyl-7-coumarylamide substrates with an arginine or phenylalanine residue adjacent to the leaving group. Maximum activity with the first group of substrates was at pH 10.5, and this activity was inhibited by leupeptin, chymostatin and Ca2+. Maximum activity with the latter group of substrates was at pH 7.5, and was also inhibited by the two microbial inhibitors, but was activated by Ca2+ ions. By using [14C]methylcasein as a substrate, maximum activity was observed at pH9.0, and this proteolytic activity was not affected by leupeptin, was enhanced by chymostatin and inhibited by Ca2+. Similar effects were observed when benzyloxycarbonyl-Leu-Leu-Glu 2-naphthylamide was used as a substrate. These enzymic activities were abolished by p-hydroxymercuribenzenesulphonic acid or mersalyl acid, whereas a small activation was observed with cysteine or dithiothreitol.

An economic volt-hour integrator, compatible with commercial and homemade electrophoresis power supplies

In isoelectric focusing systems--a technique widely used for separation and characterization of proteins--the value of the volt-hour integral required to achieve steady-state focusing conditions differs markedly for different proteins. A convenient method to measure the correct volt-hour integral for a given protein, thereby assuring intra- and interlaboratory reproducibility of experiments, can be performed with a volt-hour integrator. As commercially available integrators are compatible only with the power supply marketed by the same manufacturer, a volt-hour integrator was designed which can be used in conjunction with any commercial or homemade power supply. This simple, low-cost integrator is expected to be of interest to those researchers who have so far refrained from introducing volt-hour integration, due to incompatibility of commercial volt-hour integrators with their isoelectric focusing system.

Loss of fast-twitch isomyosins in skeletal muscles of the diabetic rat

By means of pyrophosphate electrophoresis the myosin isoenzyme pattern of two fast-twitch skeletal muscles (extensor digitorum longus, gastrocnemius) and one slow-twitch muscle (soleus) was investigated in control rats and was compared with that of rats 4 weeks after induction of diabetes mellitus by streptozotocin injection. In the fast-twitch muscles the isomyosin pattern consisting of FM1 (fast isomyosin 1), FM2 and FM3 was strongly affected by diabetes, resulting in an extensive loss of FM1 and a substantial decrease of FM2. These changes were also apparent when the light chains of the fast isomyosins were analysed by two-dimensional electrophoresis: LC3f (myosin light chain 3f) largely disappeared and LC2f was significantly diminished. In contrast, the isomyosin pattern in soleus muscle, consisting of SM1 (slow isomyosin 1) and SM2, was not affected by the diabetic state, and two-dimensional electrophoresis revealed a normal light-chain pattern of LC1sa, LC1sb and LC2s. These results indicate that the isomyosins of slow-twitch oxidative myofibres are more resistant to the hormonal and metabolic disorders during diabetes mellitus than are the isomyosins of fast-twitch fibres.

Identification of four distinct serine proteinase inhibitors in rat skeletal muscle

The serine proteinase inhibitory capacity in the cytosolic fraction of rat skeletal muscle tissue is accounted for by several discrete inhibitory activities. Three of these activities are identical with the proteinase inhibitors alpha 1-proteinase inhibitor, rat proteinase inhibitor I and rat proteinase inhibitor I I respectively, which have been recently characterized as major serine proteinase inhibitors in rat serum (Kuehn, L., Rutschmann, M., Dahlmann, B. and Reinauer, H. (1984) Biochem. J. 218, in the press). The other inhibitor molecule, having an Mr of about 15 000, appears to be an endogenous inhibitor.

Proteinase inhibitors in rat serum. Purification and partial characterization of three functionally distinct trypsin inhibitors

Three different serine proteinase inhibitors were isolated from rat serum and purified to apparent homogeneity. One of the inhibitors appears to be homologous to alpha 1-proteinase inhibitor isolated from man and other species, but the other two, designated rat proteinase inhibitor I and rat proteinase inhibitor II, seem to have no human counterpart. alpha 1-Proteinase inhibitor (Mr 55000) inhibits trypsin, chymotrypsin and elastase, the three serine proteinases tested. Rat proteinase inhibitor I (Mr 66000) is active towards trypsin and chymotrypsin, but is inactive towards elastase. Rat proteinase inhibitor II (Mr 65000) is an effective inhibitor of trypsin only. Their contributions to the trypsin-inhibitory capacity of rat serum are about 68, 14 and 18% for alpha 1-proteinase inhibitor, rat proteinase inhibitor I and rat proteinase inhibitor II respectively.

Susceptibility of muscle soluble proteins to degradation by mast cell chymase

We investigated the in vitro susceptibility of muscle soluble proteins to the major alkaline proteinase (chymase) from skeletal muscle tissue, an enzyme originating from intramuscular mast cells, but also present in certain muscle fibers. Cytoplasmic proteins from rat skeletal muscle tissue were fractionated into four groups according to their different isoelectric points: fraction A (pI 9.5-7.0), B (pI 7.0-5.6), C (pI 5.5-4.5) and D (pI 5.3-3.5). Chromatography of these fractions on octyl-Sepharose CL-4B revealed the presence of a higher percentage of hydrophobic proteins in fraction C and D as compared to fraction A and B. In vitro degradation of these protein fractions by chymase, isolated from rat skeletal muscle tissue, was monitored (a) by measuring the ability of these proteins to bind Coomassie G-250, and (b) by analyzing the digestion mixture in isoelectric focusing gels. Both methods revealed fraction B proteins to be degraded very rapidly. While there was also a significant breakdown of fraction A proteins, fraction C and D proteins were degraded only very slowly, if at all. These differences in degradability are not due to the presence of a proteinase inhibitor in fraction C and D. The results suggest that mast cell chymase preferentially degrades those groups of muscle soluble proteins, the constituents of which have neutral to basic isoelectric points and a relatively low surface hydrophobicity.

Identification of three high molecular mass cysteine proteinases from rat skeletal muscle

Three cysteine proteinases were isolated from the post-myofibrillar fraction of rat skeletal muscle. Proteinase I preferentially hydrolyzes Z-Phe-Arg-NMec with pH optimum at 8-9. The enzyme activity is stabilized by ATP against thermal inactivation. Proteinase II and III were not resolved by anion-exchange chromatography, by affinity chromatography on Arginine-Sepharose or by gel filtration. Proteinase II, splitting Bz-Val-Gly-Arg-NMec optimally at pH 10-10.5, is inactivated by ATP, whereas Proteinase III, hydrolyzing Suc-Ala-Phe-NMec at pH 7-7.5 is not affected by the nucleotide. The molecular mass of proteinase I is about 750 000 and that of proteinase II and III is about 650 000, as determined by gel filtration.

Immunohistochemical localization of two proteinases in skeletal muscle

Immunohistochemical localizations of cytosolic and myofibrillar proteinases revealed a different myofiber locale for each enzyme in the rat. Although the cytosolic proteinase was most pronounced in mast cells within soleus and extensor digitorum longus (EDL) muscles, certain fibers of the EDL were also positive. The myofibrillar proteinase, on the other hand, appeared to be present in interstitial spaces between muscle fibers in the EDL but conversely present in some fibers of the soleus muscle.

Studies on proteolytic activities in heart muscle of diabetic rats

Induction of diabetes mellitus in rats following injection of streptozotocin caused reduction in rate of gain of heart weight, of protein and of DNA content in the first two weeks. During the same time interval the overall activity of acid proteinases (cathepsin D), of alkaline proteinases and of proteinase inhibitors was measured in heart muscle homogenates. No statistically significant differences were detected compared with the proteinase activities in control rats. In contrast, total aminopeptidase activity in diabetic hearts was consistently lower than in control hearts. Earlier studies on rat skeletal muscles have shown that induction of diabetes mellitus is followed by a substantial increase of alkaline proteinase as well as aminopeptidase activities. These findings are contrasted by present data obtained with heart muscle of diabetic rats, suggesting that this tissue responds differently to insulin deficiency.

Isolation and characterization of three different forms of arylamidase from rat skeletal muscle

An arylamidase hydrolysing L-leucine-4-nitroanilide was extracted from rat skeletal muscle homogenate and purified by means of anion-exchange chromatography on DEAE-Sephadex A-50 followed by gel filtration on Sephadex G-150 and Sepharose 6B. The enzyme was isolated in the form of three different protein complexes that differ in molecular weight, kinetic data, and sensitivity to metal ions. As studied by SDS-gel electrophoresis and repeated gel chromatography on Sepharose 6B these forms are: 1, a stable monomer (A1) of Mr 122000; 2. A stable dimer (A2) of Mr 244000; and 3. a stable polymer (A3) of more than Mr 4.10(6). The arylamidase was optimally active at pH 7.3 and did not require metal ions. Treatment with 1,10-phenanthroline resulted in complete inactivation, the activity could be restored by the addition of manganous chloride. The sulphhydryl-blocking reagent 4-hydroxymercuribenzoate strongly inactivated the arylamidase, this inhibition could be reversed by the addition of 2-mercaptoethanol. Addition of phenylmethylsulfonyl fluoride had no effect on the enzyme activity. Furthermore, the influence of metal ions as well as the substrate specificity were investigated and compared for all three forms of arylamidase.

Antagonistic effects of endurance training and testosterone on alkaline proteolytic activity in rat skeletal muscles

Endurance swimming training for 8 weeks led to an increase by about 50% of alkaline proteinase activity in musculus extensor digitorum longus and about 10% in musculus soleus of normal male rats as compared to sedentary control rats. This exercise-mediated increase of proteolytic activity was prevented by the simultaneous administration of 10 mg testosterone propionate/kg body weight twice a week. The data suggest that testosterone has a regulatory effect on the alteration of the protein-degradative mechanism during endurance training.

The influence of testosterone on the alkaline proteolytic activity in rat skeletal muscle

The effects of testectomy and subsequent administration of testosterone propionate on the activity of the alkaline proteinases in rat skeletal muscle were investigated. Castration of the mature rat was followed by a short-term delay in protein accretion in skeletal muscle tissue as measured by the protein/DNA ratio and was paralleled by a 2-3-fold increase in specific activity of the alkaline proteinase(s). This increase of proteolytic activity was equally significant when expressed relative to microgram DNA. Although the gain in body weight was significantly lower in the castrated rats, nevertheless the protein/DNA ratio in muscle after 6 weeks approximated the values of sham-operated control rats without normalization of the proteolytic activity. Treatment of the castrated rats with testosterone propionate resulted in restoring normal levels of previously elevated levels of alkaline proteolytic activity in muscle tissue. The normalization of enzyme activity as well as protein accretion in muscle was dose-dependent. Treatment of the rats with a low dose (0.1 mg/day) of testosterone propionate failed to restore the proteolytic activity, but led to a small increase of th protein/DNA ratio as well as to a progressive increase in body weight. These data indicate a regulatory role of testosterone in the adaptive behaviour of the alkaline proteolytic system in rat skeletal muscle.

Purification and some properties of an alkaline proteinase from rat skeletal muscle

1. Rat skeletal muscle was homogenized in 0.05M-Tris/HCl, pH 8.5, containing 1M-KCl. Myofibrillar proteins were precipitated by addition of (NH4)2SO4 (33% saturation). 2. The alkaline proteolytic activity that was precipitated with the myofibrillar proteins was solubilized with trypsin (conjugated to Sepharose) and further purified by affinity chromatography, ion-exchange chromatography and gel filtration. 3. The purified enzyme migrates as a single band in polyacrylamide-disc electrophoresis, and has optimum hydrolytic activity with azocasein and [14C]haemoglobin as substrates at pH 9.4 and 9.6 respectively. Its apparent molecular weight, as determined by gel filtration on Sephadex G-75, is 30800. 4. The purified alkaline proteinase is strongly inhibited by equimolar amounts of soya-bean trypsin inhibitor and ovomucoid, whereas di-isopropyl phosphorofluoidate and alpha-toluenesulphonyl fluoride have no effect. On the other hand N-ethylmaleimide and p-chloromercuribenzoate have inhibitory effects on the enzyme activity. 5. Bivalent metal ions (Fe2+, Co2+, Zn2+, Mg2+, Mn2+) diminish the proteolytic activity, at 1mM concentrations. Ca2+ ions and the metal-ion-chelating agent EDTA are without effect on enzyme activity. 6. The enzyme is part of the alkaline proteolytic activity that appears to be associated with myofibrillar proteins.

Insulin effect on proteolytic activities in rat skeletal muscle

Proteolytic activity has been measure in rat skeletal muscle by use of [14C]-hemoglobin as substrate. The activity of the alkaline proteinases increases during starvation and in diabetic state. In streptozotocin-diabetic animals the activity of alkaline proteases increases to 300% over a time of 21 days. Insulin treatment reverses the enhanced enzyme activity to normal level.