Actomyosin myofibrillar proteins

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,... 

Actomyosin. At high salt concentrations ( . . 0.6 M KC1), actin and myosin combine to form actomyosin filaments giving a highly viscous solution. Actomyosin retains the ATPase activity of myosin and demonstrates "super-precipitation" on the addition of ATP (24,34). As expected, there are differences between actomyosins of rabbit and fish with respect to solubility (10,22,35,36), viscosity (46) and ultracentrifugal behavior (477. Since actomyosin is the most readily available form of myofibrillar proteins from fish muscle, its behavior relative to deterioration during frozen storage has been most frequently studied. 

A number of the proteins constituting Z lines have been reported, but unfortunately their structural roles have not been worked out in detail. a-Actinin (95 kDa x 2) was the first discovered Z-line protein that is most abundant in Z lines (2% of the total myofibrillar protein) (Ebashi and Ebashi, 1965). a-Actinin was discovered as a protein factor promoting contraction of actomyosin (Ebashi et al., 1964). a-Actinin is also the first example of an actin-gelating protein (Maruyama and Ebashi, 1965). Granger and Lazarides (1978) showed that a-actinin is uniformly... 

Electron Microscopy. Examination of fish proteins by electron microscopy conclusively shows that actomyosin aggregates during frozen storage (59,63,69). The change in structures of the extracted myofibrillar proteins and of the myofibril residues of frozen-stored cod muscle was studied by electron microscopy. The decrease in the number of actomyosin filaments and an increase in the number and size of large aggregate were found (69). Unfrozen carp actomyosin, either dissolved in 0.6M KC1 or suspended in 0.05M KC1, exists in a typical arrowhead... 

A role for MAPK in the contractile responsiveness of smooth muscle may result from either of two possible mechanisms, both involving caldesmon phosphorylation. First, caldesmon phosphorylation by MAPK may lead directly to an alteration of actomyosin activity. Caldesmon may exert this effect alone, or in concert with other myofibrillar proteins such as cal-ponin. Second, phosphorylation of caldesmon may alter the dynamics of actin filament organization within the cell. Caldesmon phosphorylation may result in alterations of the cellular cytoskeleton that must occur during prolonged contractions. 

Lawrie (1985) classified meat proteins into three types salt-soluble (myofibrillar) proteins, water-soluble (sarcoplasmic) proteins, and insoluble connective tissue proteins. The myofibrillar proteins actin, myosin and actomyosin are the major proteins responsible for determining the heat stability of comminuted meat emulsions. 

Muscle proteins have traditionally been grouped into three categories based on their solubility the sarcoplasmic proteins (consisting mainly of enzymes), myofibrillar proteins (actin, myosin, tropomyosin, troponin, etc.) and connective tissue (mainly collagen). The mixture of myosin, actin, tropomyosin, troponins and other myofibrillar proteins is called actomyosin (AM). Myofibrillar proteins contribute significantly to the technological properties of fish and meat [1-2,5-8]. 

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