Muscle soluble protein

Martin, R., Azcona, J.I., Casas, C., Hamandez, P.E., and Sanz, B. 1988. Sandwich ELISA for detection of pig meat in raw beef using antisera to muscle soluble proteins. J. Food Prot. 51,190-194. 

As hormone-sensitive lipase hydrolyzes triacylglyc-erol in adipocytes, the fatty acids thus released (free fatty acids, FFA) pass from the adipocyte into the blood, where they bind to the blood protein serum albumin. This protein (Mv 66,000), which makes up about half of the total serum protein, noncovalently binds as many as 10 fatty acids per protein monomer. Bound to this soluble protein, the otherwise insoluble fatty acids are carried to tissues such as skeletal muscle, heart, and renal cortex. In these target tissues, fatty acids dissociate from albumin and are moved by plasma membrane transporters into cells to serve as fuel. 

Before selecting a method to measure a specific aspect of protein functionality, one must decide on the complexity of the testing matrix. Researchers have used a single purified protein, a crude extract of proteins, a prototype food product, or an actual product to study protein functionality. For meat studies, formulated meat systems, ground muscle, myofibrillar proteins, salt-soluble proteins, actomyosin,... 

Dambergs, N. (1963). Extractives of fish muscle. 3. Amounts, sectional distribution and variations of fat, water-solubles, protein and moisture in cod fillets. Journal of the Fisheries Research Board of Canada 20,909-918. 

Large pieces are reassembled into whole products, ranging fi-om joints, tp aligned flake products, to the ubiquitous burger. All these processes require that the particles adhere to one another. Adhesives, such as egg white or other soluble proteins and gelling polysaccharides can be added, but most frequently, muscle proteins themselves... 

Glyceraldehyde-3-phosphate dehydrogenase occurs widely and abundantly throughout nature. It comprises about 20% of the total soluble protein in yeast (10) and up to 10% of the soluble protein from muscle... 

The alpha helix represents the second major structural element of soluble proteins and is also found in many fibrous proteins, including those of muscle... 

Fig. 7. Influence of pH on the extractability of the muscle proteins of cod at ionic strength 0.85. Ordinate per cent of the total protein N extracted as soluble protein N (X), as myosin N (O), and as non-myosin (A) (after dyee, french, and SNOW, 1950).

The analyses carried out up to now on such extracts have been based upon differences of solubility (see p. 235). The discussion of the results obtained has made clear that a reinvestigation of these mixtures is necessary in order to define more accurately the structure proteins of fish muscle. Electrophoresis, which permits the analysis of such mixtures with a minimum of alteration, appears a particularly suitable method. It has been applied as yet only to carp muscle extracts of high ionic strength (Hamoir, 1951b, 1954, 1955). In view of the very constant electrochemical behavior of the muscle structure proteins (see Hamoir, 1953a), it seems safe to assume that similar results will be obtained with other fishes. The results already obtained will therefore be more extensively described. The slight difference in extractibility previously mentioned between white and red rabbit muscles (Crepax, 1952) suggests that a separate study of both fish muscles would also be desirable in this case, but it has not yet been undertaken. 

Other Proteins. Since Reay and Dyer discovered that denaturation of myofibrillar proteins is of such profound importance, little attention has been given to the water-soluble proteins including enzymes and other proteins in the sarcoplasm, subcellular organelles, and cell membranes. Recently reports have appeared on the freeze denaturation of enzymes. These studies involved enzymes such as catalase, ADH, GDH, LDH, and MDH from sources other than fish (88,89,90) and attention was given to the effectiveness of various cryoprotective substances (89, 90). Comparable studies with enzymes from fish muscle are few in number (91). Studies on fish muscle proteins must be extended to this area if a complete picture of the freeze denaturation of fish muscle is to be obtained. It should be noted that freeze stable enzymes might have important effects during frozen storage of fish (92,93). 

In the cytosol of muscle cells, the free Ca " ranges from 10 M (resting cells) to more than 10 (contracting cells), whereas the total Ca concentration In the SR lumen can be as high as 10 M. However, two soluble proteins In the lumen of SR vesicles bind Ca " and serve as a reservoir for intracellular Ca ", thereby reducing the concentration of free Ca " ions In the SR vesicles and conse-quendy the energy needed to pump Ca " ions into them from the cytosol. The activity of the muscle Ca " ATPase increases as the free Ca " concentration in the cytosol rises. Thus in skeletal muscle cells, the calcium pump in the SR membrane can supplement the activity of a similar Ca " pump located in the plasma membrane to assure that the cytosolic concentration of free Ca " in resting muscle remains below 1 jjlM. 

Solubility is one property that can be used to classify the proteins that result from the various levels of structure. For example, fibrous proteins are not soluble in water. Many familiar components of tissues are composed of fibrous proteins, including keratin (the protein present in hair), collagen (a structural protein found in tendons and cartilage), myosin (a protein found in most muscle tissue), and fibrin (the protein that allows blood to clot and form scabs). Conversely, globular proteins are soluble in water. For example, albumins are water-soluble proteins that provide a familiar example of what happens when a protein loses its secondary and tertiary structure, a process called denaturation. When an egg is cooked, the egg white changes from translucent to white this color change is indicative of the change in structure that has taken place in the albumin proteins. 

Glycogen synthase has also been purified from A. suum muscle and is about 3% of the soluble protein (5). It is converted into an inactive o-form when phosphorylated by ox heart cAMP-dependent protein kinase and binds about 1 mol of phosphate/mol of subunit. A second glycogen synthase activity has also been described and purified from... 

Rabbit muscle aldolase is the archetypical type 1 (imine-forming) aldolase and constitutes 3% of the soluble protein obtained from this source [26]. It is responsible for catalyzing the cleavage or synthesis of the carbon-carbon bond which joins carbon 3 and 4 in fructose 1,6-diphosphate (F-1,6P2) to form dihydroxyacetone... 

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