Troponins, hybrid

Ca-SensMang Activities of Various Kinds of Hybrid Troponins... 

Troponin components of bovine cardiac muscle were separated by essentially the same procedure as for skeletal troponin components (Tsukui and Ebashi, 1973). Studies on the Ca + sensitivity of superprecipitation with various combinations of troponin components from rabbit skeletal and bovine cardiac muscles showed that most hybrid troponins gave the lower Ca sensitivity of superprecipitation (Ebashi, 1974a,b) (Table III). The lowest value was obtained with the combination of skeletal troponin C-T and cardiac troponin I. However, when cardiac troponin T was combined with skeletal troponin I—C, the calcium sensitivity was exceptionally high and exceeded those obtained by the native... 

The contraction of ascidian smooth muscle was found to be regulated through the troponin-tropomyosin system. But the action of troponin components was different from that of troponin of vertebrate striated muscles (Endo and Obinata, 1981). In this system, the inhibitory action of troponin I (MW 24,000) is less remarkable compared with vertebrate skeletal troponin I, and troponin C (MW 18,000) does not neutralize the inhibition by troponin I. But upon further addition of troponin T (MW 33,000) in the concomitant presence of all three components and tropomyosin, the contractile interaction of myosin and actin is activated. In this case, the action of troponin T has some similarity with that of the above-mentioned cardiac troponin T hybridized with skeletal troponin C-I. Since actomyosin, without these regulatory proteins, is inhibited regardless of Ca concentration, Ca " and troponin-tropomyosin are activators for contraction of actomyosin in ascidian smooth muscle. In this respect, the type of Ca + regulation of ascidian smooth muscle is the same as that for vertebrate smooth muscles which do not contain troponin (Ebashi, 1980). 

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