|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1991 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1990 : ¥1,400,000 (Direct Cost : ¥1,400,000)
It is well-known that bivalve smooth adductor muscle show catch contraction, that is, an energy-saving prolonged state of contraction. In the present project, we have studied the catch mechanism from the standpoint of the participation of regulatory proteins in the catch contraction.
1. Surf-clam smooth muscle was investigated to isolate the troponin and other actin-binding proteins. This muscle seemed to lack troponin because its native thin filament and troponin fraction were incapable of conferring Ca^<2+>-sensitivity to rabbit actomyosin. However, the foot muscle possesses major 160kDa actin binding protein (ABP) which was cosedimented with actin to form turbidity. The ABP was shown to make F-cactin filaments into bundiles under physiological conditions. The molecular weight and actin-bunding property of the ABP were similar to those of caldesmon which has been considered as a candidate for "latch proteins" in vertebrate smooth muscle, however, the other characteristics of ABP were
not. Thus, the binding of ABP to F-actin was unaffected by Ca^<2+>-calmodulin and the amino acid composition of the ABP was quite different from that of caldesmon. These resu lts indicate that the APB is a different type of actin-bundling protein from caldesmon. The ABP-like proteins were shown to be present in various bivalves, such as scallop, mussel, oyster, and ribbed ark. To make clear the relationship between the actin-bundling property of ABP and the catch contraction, further physiological and biochemical studies are necessary.
2. A binary complex consisting of 19kDa troponin-I(19-Tnl)and 4OkDa troponin-T(40-TnT)was co-purified with troponin form a crude troponin fraction of akazara scallop adductor muscle. This complex is incapable of conferring Ca^<2+>-sensitivity to rabbit reconstituted actomyosin Mg-ATPase activity, but became capable on further complexing with Akazara scallop troponin-C. On hybridization with the Akazara scallop troponin subunits, the isolated 19-Tnl and 40-TnT were shown to be able to substitute for troponin-I and troponin-T, respectively. We may consider that the 19-TnIAO-Tnl binary complex is implicated in the actin-finked regulation in somehow different manner from troponin. Less