Protein in skeletal muscle

One obvious symptom of a patient suffering from trauma is loss of body weight. This is due to increased mobilisation of both triacylglycerol in adipose tissue and degradation of protein in skeletal muscle. 

GH stimulates incorporation of labelled amino acids into protein in skeletal muscle (diaphragm) from hypophysectomized rats in vitro [41,84], The effect is a consequence of stimulation of protein biosynthesis, although amino acid transport is also affected. Insulin and somatomedins also stimulate protein synthesis in diaphragm [44], but there are clear-cut differences between the actions of these hormones and of GH. Thus a 30 min lag period is characteristic of the action of GH, as is a refractory. period after 2-3 h of stimulation. 

Another very long protein (nebulin) is associated with the thin filaments. Nebulin has a molecular weight of about 700,000. An abundant protein in skeletal muscle, nebulin extends from either side of the Z-disks along the entire length of the thin filaments. It may serve as a template for thin-filament assembly, and may interact with tropomyosin, and also may have a regulatory role. 

Dystrophin, the protein product of the Duchenne muscular dystrophy locus, is a major cytoskeleton protein in skeletal muscle cells. There have been only limited studies on the use of this marker in the diagnosis of rhabdomyosarcoma. Dystrophin was found in most cases of rhabdomyosarcoma in frozen sections, and was lacking in other small cell neoplasms including lymphoma, PNET, and Wilms tumor. 

FIG. 4. Mutations in the myophosphoiylase gene in McArdle s disease. The mutations are described in the text. The most common phenotype is a complete lack of phosphorylase protein in skeletal muscle and, hence, the loss of the muscle vitamin B6 slow pool. 

Li M, Dalakas MC. (2000) Expression of human lAP-like protein in skeletal muscle An explanation for the rare incidence of muscle fiber apoptosis in T-cell mediated inflammatory myopathies. J Neuroimmunol 106, 1-5. 

Actually, two types of proton leak may be present at the mitochondrial level namely, basal proton leak and inducible proton leak. The basal type is present in mitochondria within every tissue, and may be related both to the hpid environment of the membrane and to specific proteins such as adenine nucleotide translocase (ANT) (Brand et al, 2005b Shabalina et al., 2006). The inducible type seems to be tightly regulated and is mediated by specific proteins. In skeletal muscle mitochondria, rmcoupling protein 3 (UCP3) plays a significant role in the latter process (Brand et al., 2005). 

Wigmore, P.M. and N.C. Stickland, 1983a. Muscle development in large and small pig fetuses. J. Anat. 137,235-245. Wigmore, P.M. and N.C. Stickland, 1983b. DNA, RNAand protein in skeletal muscle of large and small pig fetuses. Growth 47, 67-76. 

The sacroplasmic proteins myoglobin and hemoglobin are responsible for much of the color in meat. Species vary tremendously in the amount of sacroplasmic proteins within skeletal muscle with catde, sheep, pigs, and poultry Hsted in declining order of sarcoplasmic protein content. Fat is also an important component of meat products. The amount of fat in a portion of meat varies depending on the species, anatomy, and state of nutrition of the animal. The properties of processed meat products are greatiy dependent on the properties of the fat included. Certain species, such as sheep, have a relatively higher proportion of saturated fat, whereas other species, such as poultry, have a relatively lower proportion of saturated fat. It is well known that the characteristic davors of meat from different species are in part determined by their fat composition. 

Lnczak-Szcznrek, A., and Flisinska-Bojanowska, A., 1977. Effect of high-protein diet on glycolytic processes in skeletal muscles of exercising rats. Journal of Physiology and Pharmacology 48 119—126. 

NFAT proteins are expressed in skeletal, cardiac, and smooth muscle and play important roles in the regulation of the development and differentiation of these tissues. In skeletal muscle, NFAT isoforms are expressed at different stages of development and regulate progression from early muscle cell precursors to mature myocytes. NFAT proteins have also been shown to control the expression of the myosin heavy chain and positively regulate muscle growth [1, 2]. 

Parvalbumin is a cytosolic protein expressed mainly in skeletal muscles and brain. 

The analytic validity of an abstract parallel elastic component rests on an assumption. On the basis of its presumed separate physical basis, it is ordinarily taken that the resistance to stretch present at rest is still there during activation. In short, it is in parallel with the filaments which generate active force. This assumption is especially attractive since the actin-myosin system has no demonstrable resistance to stretch in skeletal muscle. However, one should keep in mind, for example, that in smooth muscle cells there is an intracellular filament system which runs in parallel with the actin-myosin system, the intermediate filament system composed of an entirely different set of proteins, (vimentin, desmin, etc.), whose mechanical properties are essentially unknown. Moreover, as already mentioned, different smooth muscles have different extracellular volumes and different kinds of filaments between the cells. 

Salo, D.C., Donovan, C.M., Davies, K.J, (1991). Hsp70 and other possible heat shock or oxidative stress proteins are induced in skeletal muscle, heart, and liver during exercise. Free Radic. Biol. Med 11,239-246. 

The general picture of muscle contraction in the heart resembles that of skeletal muscle. Cardiac muscle, like skeletal muscle, is striated and uses the actin-myosin-tropomyosin-troponin system described above. Unlike skeletal muscle, cardiac muscle exhibits intrinsic rhyth-micity, and individual myocytes communicate with each other because of its syncytial nature. The T tubular system is more developed in cardiac muscle, whereas the sarcoplasmic reticulum is less extensive and consequently the intracellular supply of Ca for contraction is less. Cardiac muscle thus relies on extracellular Ca for contraction if isolated cardiac muscle is deprived of Ca, it ceases to beat within approximately 1 minute, whereas skeletal muscle can continue to contract without an extraceUular source of Ca +. Cyclic AMP plays a more prominent role in cardiac than in skeletal muscle. It modulates intracellular levels of Ca through the activation of protein kinases these enzymes phosphorylate various transport proteins in the sarcolemma and sarcoplasmic reticulum and also in the troponin-tropomyosin regulatory complex, affecting intracellular levels of Ca or responses to it. There is a rough correlation between the phosphorylation of Tpl and the increased contraction of cardiac muscle induced by catecholamines. This may account for the inotropic effects (increased contractility) of P-adrenergic compounds on the heart. Some differences among skeletal, cardiac, and smooth muscle are summarized in... 

As stated above, extracellular Ca plays an important role in contraction of cardiac muscle but not in skeletal muscle. This means that Ca both enters and leaves myocytes in a regulated manner. We shall briefly consider three transmembrane proteins that play roles in this process. 

When smooth muscle myosin is bound to F-actin in the absence of other muscle proteins such as tropomyosin, there is no detectable ATPase activity. This absence of activity is quite unlike the situation described for striated muscle myosin and F-actin, which has abundant ATPase activity. Smooth muscle myosin contains fight chains that prevent the binding of the myosin head to F-actin they must be phosphorylated before they allow F-actin to activate myosin ATPase. The ATPase activity then attained hydrolyzes ATP about tenfold more slowly than the corresponding activity in skeletal muscle. The phosphate on the myosin fight chains may form a chelate with the Ca bound to the tropomyosin-TpC-actin complex, leading to an increased rate of formation of cross-bridges between the myosin heads and actin. The phosphorylation of fight chains initiates the attachment-detachment contraction cycle of smooth muscle. 

A different but very interesting scenario involving L-type Ca channels is seen in skeletal muscle, where the major component of these Ca channels plays two roles. Skeletal muscle does not require extracellular Ca for excitation-contraction coupling, rather it utilizes Ca stored in the sarcoplasmic reticulum. The role of the L-type channel proteins as true Ca channels in skeletal muscle appears to be of secondary importance, but may be to provide Ca to the cells over longer periods of time. The main role of the L-type channel protein(s)... 

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