Food Structure


D. W. Stanley


A review of the muscle cytoskeleton is presented. Current evidence leads to the concept of a muscle cell cytoskeleton consisting of at least two elements - gap filaments which are located parallel to the fiber ax~s and provide intracellular elasticity and tensile strength and intermediate filameots found in the zdisc area that function to connect adjacent Z- discs and promote lateral registration. The former constituent consists of the high molecular weight protein connectin (titinl while the latter is composed of the smaller protein desmin (skeletinl. Both proteins exist in filamentous form, are susceptible to proteolysis and are insoluble in physiological solutions . It is proposed that these two elements may interact in the region of t he Z- disc to f o rm a three dimensional network that functions to hold myofibrils in place and provide an ordering of the contractile mechanism . Degradation o f the cytoskeleton during post-mortem conditioning of muscle may be partially responsible for the tenderizing phenomenon observed in aged meat. Original work is described in which beef skeletal muscle cell segments are induced to empty, leaving behind the sarcolemmal sheath . Conditions necessary for this reaction to occur included the presence of Ca++ ions and six days of post -mortem conditioning at 0-5°C. On the basis of these data, it is further proposed that muscle cell emptying may be a consequence of the action of an endogenous proteolytic enzyme that breaks down the cytoskeleton.

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