Properties of calponin isolated from sheep aorta thin filaments

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 mg/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, Ca2+ or Ca2+ calmodulin. Caldesmon inhibited actomyosin with a 10-fold greater potency than calponin in the presence of tropomyosin and inhibition could be reversed by Ca2+ calmodulin under certain conditions. Calponin had no effect on caldesmon inhibition or the reversal of inhibition.