REGULATED CROSS-LINKED ACTIN-FILAMENTS AND THE DECOUPLING BETWEEN THEIR ATPASE ACTIVITY AND SLIDING MOTILITY

Troponin-tropomyosin complex from skeletal muscles was observed to reg ulate sliding movement of actin filaments on myosin molecules in a man ner independent of their ATPase activity. When actin molecules were cr osslinked with DSS (disuccinimidyl suberate), the myosin ATPase activi ty in the presence of the modified actin filaments complexed with both troponin and tropomyosin was only 10% less than that in the case of u nmodified actin, and the ATPase activation was independent of calcium ions. In contrast, the sliding velocity of the modified actin filament s on myosin molecules decreased to zero below pCa 6.5. The present res ults indicate that troponin-tropomyosin complex regulates contractile movement of actomyosin systems through direct alternation of a mechano chemical property of the thin filaments, not through a decrease in the ATPase activity of the myosin molecules.