in our previous model [ hill , t. l. , eisenberg , e. & greene , l. e. ( 1980 ) proc . natl . acad . sci . usa 77 , 3186-3190 ] , we assumed that each tropomyosin unit , including one troponin-tropomyosin molecule and seven actin sites on the actin filament , could exist in two conformational states which presumably differed in the position of the tropomyosin on the actin .
C0025979
actin
C0001271
actin