Food Structure


Myofibrils were isolated from atdeath ovin elongissimus muscles and incubated with crude calcium activated factor prepared from the same muscle and with purified cathepsin D. Myofibrils we reincubated with these enzymes separately (first incubation) and successively (second incubation). The major changes induced by cathepsin D first incubation include degradation of myofibrillar proteins with molecular weight > 200 K, myosin, actin, troponin- T and troponin 1. Also new bands appeared at the 140- 160 K, 80 K, 68 K and 30 K regions. Similar changes were obtained 1v hen myofibrils were incubated first with CAF then with cathepsin D (second incubation). On the other h and CAF first incubation resulted in the degradation of the high molecular weight proteins ( > 200 K), desmin, troponin T , troponin I and it released a -actinin. Also new bands appeared immediately below C-protein (140 K) , 95 K and 30 K. Unlike cathepsin D, CAF did not affect myosin or actin. However, when myofibrils were first incubated with cathepsin D then wit h CAF (second incubation) the latter was able to degrade actin to a much greater degree than cathepsin D. Both enzymes were able to affect the Z-lines of the myofibrils.

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