aorta thin filaments

Received 18 July 1991 Calponin, a 35 kDa actin-binding protein, was shown to be a normal component of 'native' thin filaments prepared from sheep aorta. Actin, tropomyosin, caldesmon and calponin were present in molar ratios 14 : 2 : 1 : 0.9. Calponin was isolated from thin filaments in yield 0.5 rag/100 mg thin filament protein. Calponin inhibited actomyosin ATPase up to 85%, half maximal at 0.2 calponin/actin. Inhibition did not depend on tropomyosin. Ca z• or Ca -'+.calmodulin, Caldesmon inhibited actomyosin with a I 0-fold greater potency than calponin in the presence of tropomyo- sin and inhition could be reversed by Ca".calmodulin under certain conditions. Calponin had no effect on caldesmon inhibition or the reversal of inhibition. Smooth muscle; Caldesmon; Calmodulin; Calponin; Thin filament; Actomyosin