Myofibrillar protein degradation after eccentric exercise

Summary Male rats were run downhill for 90 minutes (nonexhaustive). Following the exercise, muscle protein degradation was increased, as determined by urinary 3-methylhistidine. However, minimal changes were observed in the relative percentage of the minor myofibrillar proteins and in the protease calcium activated factor in the long head of the triceps brachii muscle (eccentrically exercised) following the exercise bout.     

Regulated protein degradation in mitochondria

Various adenosine triphosphate (ATP)-dependent proteases were identified within mitochondria which mediate selective mitochondrial protein degradation and fulfill crucial functions in mitochondrial biogenesis. The matrix-localized PIM1 protease, a homologue of theEscherichia coli Lon protease, is required for respiration and maintenance of mitochondrial genome integrity. Degradation of non-native polypeptides by PIM1 protease depends on the chaperone activity of the mitochondrial Hsp70 system, posing intriguing questions about the relation between the proteolytic system and the folding machinery in mitochondria. The mitochondrial inner membrane harbors two ATP-dependent metallopeptidases, them- and thei-AAA protease, which expose their catalytic sites to opposite membrane surfaces and cooperate in the degradation of inner membrane proteins. In addition to its proteolytic activity, them-AAA protease has chaperone-like activity during the assembly of respiratory and ATP-synthase complexes. It constitutes a quality control system in the inner membrane for membrane-embedded protein complexes.     

Genetic analysis of ubiquitin-dependent protein degradation

Selective degradation of cellular proteins serves to eliminate abnormal proteins and to mediate the turnover of certain short-lived proteins, many of which have regulatory functions. In eukaryotes a major pathway for selective protein degradation is ATP-dependent and is mediated by the ubiquitin system. This pathway involves substrate recognition by components of a ubiquitin-protein ligase system, covalent attachment of ubiquitin moieties to proteolytic substrates, and subsequent degradation of these conjugates by a multicatalytic protease complex. Recent genetic evidence suggests that the remarkable selectivity of this process is largely controlled at the level of substrate recognition by the ubiquitin ligase system. InSaccharomyces cerevisiae, ubiquitin-conjugating enzymes UBC1, UBC4 and UBC5 have been identified as key components of this highly conserved degradation pathway. Genetic analysis indicates that ubiquitin-dependent proteolysis is essential for cell viability and that UBC4 and UBC5 enzymes are essential components of the eukaryotic stress response.     

Proteases and protein degradation inEscherichia coli

InE. coli, protein degradation plays important roles in regulating the levels of specific proteins and in eliminating damaged or abnormal proteins.E. coli possess a very large number of proteolytic enzymes distributed in the cytoplasm, the inner membrane, and the periplasm, but, with few exceptions, the physiological functions of these proteases are not known. More than 90% of the protein degradation occurring in the cytoplasm is energy-dependent, but the activities of mostE. coli proteases in vitro are not energy-dependent. Two ATP-dependent proteases, Lon and Clp, are responsible for 70–80% of the energy-dependent degradation of proteins in vivo. In vitro studies with Lon and Clp indicate that both proteases directly interact with substrates for degradation. ATP functions as an allosteric effector promoting an active conformation of the proteases, and ATP hydrolysis is required for rapid catalytic turnover of peptide bond cleavage in proteins. Lon and Clp show virtually no homology at the amino acid level, and thus it appears that at least two families of ATP-dependent proteases have evolved independently.     

Autophagy and other vacuolar protein degradation mechanisms

Autophagic degradation of cytoplasm (including protein, RNA etc.) is a non-selective bulk process, as indicated by ultrastructural evidence and by the similarity in autophagic sequestration rates of various cytosolic enzymes with different half-lives. The initial autophagic sequestration step, performed by a poorly-characterized organelle called a phagophore, is subject tofeedback inhibition by purines and amino acids, the effect of the latter being potentiated by insulin and antagonized by glucagon. Epinephrine and other adrenergic agonists inhibit autophagic sequestration through a prazosin-sensitive ₁-adrenergic mechanism. The sequestration is also inhibited by cAMP and by protein phosphorylation as indicated by the effects of cyclic nucleotide analogues, phosphodiesterase inhibitors and okadaic acid.Asparagine specifically inhibits autophagic-lysosomal fusion without having any significant effects on autophagic sequestration, on intralysosomal degradation or on the endocytic pathway. Autophaged material that accumulates in prelysosomal vacuoles in the presence of asparagine is accessible to endocytosed enzymes, revealing the existence of an amphifunctional organelle, the amphisome. Evidence from several cell types suggests that endocytosis may be coupled to autophagy to a variable extent, and that the amphisome may play a central role as a collecting station for material destined for lysosomal degradation.Protein degradation can also take place in a salvage compartment closely associated with the endoplasmic reticulum (ER). In this compartment unassembled protein chains are degraded by uncharacterized proteinases, while resident proteins roturn to the ER and assembled secretory and membrane proteins proceed through the Golgi apparatus. In thetrans-Golgi network some proteins are proteolytically processed by Ca²⁺-dependent proteinases; furthermore, this compartment sorts proteins to lysosomes, various membrane domains, endosomes or secretory vesicles/granules. Processing of both endogenous and exogenous proteins can occurr in endosomes, which may play a particularly important role in antigen processing and presentation. Proteins in endosomes or secretory compartments can either be exocytosed, or channeled to lysosomes for degradation. The switch mechanisms which decide between these options are subject to bioregulation by external agents (hormones and growth factors), and may play an important role in the control of protein uptake and secretion.     

Genetic analysis of ubiquitin-dependent protein degradation.

Selective degradation of cellular proteins serves to eliminate abnormal proteins and to mediate the turnover of certain short-lived proteins, many of which have regulatory functions. In eukaryotes a major pathway for selective protein degradation is ATP-dependent and is mediated by the ubiquitin system. This pathway involves substrate recognition by components of a ubiquitin-protein ligase system, covalent attachment of ubiquitin moieties to proteolytic substrates, and subsequent degradation of these conjugates by a multicatalytic protease complex. Recent genetic evidence suggests that the remarkable selectivity of this process is largely controlled at the level of substrate recognition by the ubiquitin ligase system. In Saccharomyces cerevisiae, ubiquitin-conjugating enzymes UBC1, UBC4 and UBC5 have been identified as key components of this highly conserved degradation pathway. Genetic analysis indicates that ubiquitin-dependent proteolysis is essential for cell viability and that UBC4 and UBC5 enzymes are essential components of the eukaryotic stress response.     

Autophagy and other vacuolar protein degradation mechanisms.

Autophagic degradation of cytoplasm (including protein, RNA etc.) is a non-selective bulk process, as indicated by ultrastructural evidence and by the similarity in autophagic sequestration rates of various cytosolic enzymes with different half-lives. The initial autophagic sequestration step, performed by a poorly-characterized organelle called a phagophore, is subject to feedback inhibition by purines and amino acids, the effect of the latter being potentiated by insulin and antagonized by glucagon. Epinephrine and other adrenergic agonists inhibit autophagic sequestration through a prazosin-sensitive alpha 1-adrenergic mechanism. The sequestration is also inhibited by cAMP and by protein phosphorylation as indicated by the effects of cyclic nucleotide analogues, phosphodiesterase inhibitors and okadaic acid. Asparagine specifically inhibits autophagic-lysosomal fusion without having any significant effects on autophagic sequestration, on intralysosomal degradation or on the endocytic pathway. Autophaged material that accumulates in prelysosomal vacuoles in the presence of asparagine is accessible to endocytosed enzymes, revealing the existence of an amphifunctional organelle, the amphisome. Evidence from several cell types suggests that endocytosis may be coupled to autophagy to a variable extent, and that the amphisome may play a central role as a collecting station for material destined for lysosomal degradation. Protein degradation can also take place in a 'salvage compartment' closely associated with the endoplasmic reticulum (ER). In this compartment unassembled protein chains are degraded by uncharacterized proteinases, while resident proteins return to the ER and assembled secretory and membrane proteins proceed through the Golgi apparatus. In the trans-Golgi network some proteins are proteolytically processed by Ca(2+)-dependent proteinases; furthermore, this compartment sorts proteins to lysosomes, various membrane domains, endosomes or secretory vesicles/granules. Processing of both endogenous and exogenous proteins can occur in endosomes, which may play a particularly important role in antigen processing and presentation. Proteins in endosomes or secretory compartments can either be exocytosed, or channeled to lysosomes for degradation. The switch mechanisms which decide between these options are subject to bioregulation by external agents (hormones and growth factors), and may play an important role in the control of protein uptake and secretion.     

Proteases and protein degradation in Escherichia coli.

In E. coli, protein degradation plays important roles in regulating the levels of specific proteins and in eliminating damaged or abnormal proteins. E. coli possess a very large number of proteolytic enzymes distributed in the cytoplasm, the inner membrane, and the periplasm, but, with few exceptions, the physiological functions of these proteases are not known. More than 90% of the protein degradation occurring in the cytoplasm is energy-dependent, but the activities of most E. coli proteases in vitro are not energy-dependent. Two ATP-dependent proteases, Lon and Clp, are responsible for 70-80% of the energy-dependent degradation of proteins in vivo. In vitro studies with Lon and Clp indicate that both proteases directly interact with substrates for degradation. ATP functions as an allosteric effector promoting an active conformation of the proteases, and ATP hydrolysis is required for rapid catalytic turnover of peptide bond cleavage in proteins. Lon and Clp show virtually no homology at the amino acid level, and thus it appears that at least two families of ATP-dependent proteases have evolved independently.     

Intracellular protein degradation in mammalian cells: recent developments

In higher organisms, dietary proteins are broken down into amino acids within the digestive tract but outside the cells, which incorporate the resulting amino acids into their metabolism. However, under certain conditions, an organism loses more nitrogen than is assimilated in the diet. This additional loss was found in the past century to come from intracellular proteins and started an intensive research that produced an enormous expansion of the field and a dispersed literature. Therefore, our purpose is to provide an updated summary of the current knowledge on the proteolytic machinery involved in intracellular protein degradation and its physiological and pathological relevance, especially addressed to newcomers in the field who may find further details in more specialized reviews. However, even providing a general overview, this is an extremely wide field and, therefore, we mainly focus on mammalian cells, while other cells will be mentioned only for comparison purposes.     

Ventral motor neuron alterations in rat spinal cord after chronic exercise

Summary The observed differences in the soma and nuclear diameters reflect chronic changes specific to each exercise regimen used.This study was supported by National Institute of Health Grant HD 03918, Michigan State University, East Lansing, Michigan.Acknowledgments. Gratitude is expressed to Barbara Wheaton for her technical assistance in the processing of tissues and R. E. Carrow for making his laboratory facilities available for this study.     

Myofibrillar ATP-splitting in the elementary contractile cycle of an insect flight muscle

Zusammenfassung In glyzerinierten fibrillären Muskelfasern vonLethocerus werden schon 20 msec nach maximaler «Dehnungsaktivierung» der ATP-ase (um 5000%) 2 Mol ATP pro Mol Myosin gespalten, worauf die Kontraktionsspannung mit der Wechselzahl von Myosin-ATPase und Querbrücken (etwa 10 Hz) oszilliert.     

Deoxyribonucleic acid synthesis in the heart mitochondria after acute and exhaustive exercise

Resumen Las mitocondrias del corazón de ratas sometidas a natación forzada muestran filamentos considerados morfológicamente como de ADN y captan timidina tritiada. Sobre la base de estas observaciones se sugiere que las mitocondrias miocárdicas con capaces de una activa síntesis de ADN como respuesta a requirimientos funcionales agudos.     

Myofibrillar ATPase activities of red and white myotomal muscles of marine fish

Zusammenfassung Die Ca⁺⁺-und nicht-Ca⁺⁺-abhängige ATPase-Aktivität von isolierten Myofibrillen der roten und weissen Muskeln von drei Meerfischen wurde gemessen und festgestellt, dass die weissen Muskeln eine höhere Aktivität besitzen.

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I. A. Johnston was in receipt of a Science Research Council Research Studentship.

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This work was also supported by a Natural Environment Research Council grant to Dr.G. Goldspink.     

Delta opioid receptors recycle to the membrane after sorting to the degradation path

Soon after internalization delta opioid receptors (DOPrs) are committed to the degradation path by G protein-coupled receptor (GPCR)-associated binding protein. Here we provide evidence that this classical post-endocytic itinerary may be rectified by downstream sorting decisions which allow DOPrs to regain to the membrane after having reached late endosomes (LE). The LE sorting mechanism involved ESCRT accessory protein Alix and the TIP47/Rab9 retrieval complex which supported translocation of the receptor to the TGN, from where it subsequently regained the cell membrane. Preventing DOPrs from completing this itinerary precipitated acute analgesic tolerance to the agonist DPDPE, supporting the relevance of this recycling path in maintaining the analgesic response by this receptor. Taken together, these findings reveal a post-endocytic itinerary where GPCRs that have been sorted for degradation can still recycle to the membrane.     

Protein synthesis and cyclic GMP content in rat cardiac muscle after swimming exercise

Summary Rats were exercised for 6 h by swimming. Phenylalanine incorporation into myocardial proteins was increased when 2 h had elapsed after the termination of exercise. Cyclic GMP concentration did not change during the experiment, which indicates that cyclic GMP does not act directly as a trigger of myocardial protein synthesis in volume overload.     

Protein synthesis and cyclic GMP content in rat cardiac muscle after swimming exercise

Rats were exercised for 6 h by swimming. Phenylalanine incorporation into myocardial proteins was increased when 2 h had elapsed after the termination of exercise. Cyclic GMP concentration did not change during the experiment, which indicates that cyclic GMP does not act directly as a trigger of myocardial protein synthesis in volume overload.