Tropomyosin degradation

Calcium-activated protease in muscle The enz)one catalyzes the hydrolysis of troponin to tropomyosin. The enzyme is thought to be used in the degradation and turnover of muscle fibers. 

A stepwise degradation of the tropomyosin complex thus occurs in the course of the extraction, leading to a progressive increase of solubility and allowing the identification of more or less different fractions. The particle described by Bailey (1948) corresponds to the final step of this transformation. Tropomyosin may actually exist in fish muscle as a ribonucleoprotein but as the ultracentrifugal behavior typical of nucleotropomyosin is ob-... 

Kim (94) has demonstrated the degradation of myofibrillar proteins purified from porcine semimembranosus muscle by porcine leukocyte lysosomal proteinases. Troponin treated with leukocyte lysosomal pro-teinases mixed with tropomyosin did not result in the normal increase in viscosity of this system. The emulsifying capacity of aetomyosin treated with lysosomal proteinases at 37 °C and pH 7 for 12 hr was higher than that of aetomyosin incubated without enzymes. On the other hand, aetomyosin treated with papain had low emulsifying capacity because of extensive degradation. Control aetomyosin incubated at 37 °C, pH 7 for 12 hr formed a gel after removal of KC1, but aetomyosin treated with lysosomal proteinases or papain did not gel. 

Troponin is the regulatory complex of three proteins of the thin filament of myocytes. Troponin T binds to tropomyosin, troponin I is an inhibitory protein, and troponin C binds to calcium needed for muscle contraction. Following irreversible myocyte damage, unbound troponin subunits are initially released into blood from the cytosolic pools. This is followed by a sustained release of the tri-troponin complex due to the breakdown of the myocyte itself. Once in blood, the complex is further degraded into the binary troponin I-C complex, and frees troponin T. Figure 92.1 shows the kinetics of troponin subunit release. Troponin is superior to the other biomarkers for cardiac injury for two... 

In addition to phosphorylation of key regulatory enzymes of intermediary metabolism, some of the proteins involved in muscle contraction undergo a similar phosphorylation (Perry, 1979), although the role of such modification is not well understood at this moment. Examples of this are tropomyosin (Mak et al, 1978), the myosin light chains, and multiple sites within the troponin system. Functions for phosphorylation of such proteins, such as modulation of the contractile event (Perry, 1979) or regulation of proteolytic degradation rates (Toyo-Oka, 1982), have been proposed. 

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