EFFECT OF 67 KDA CALCIMEDIN ON CALDESMON FUNCTIONING

Interaction of smooth muscle caldesmon with calmodulin, troponin C,S-1 00 protein and 67 kDa calcimedin was analyzed. Native gel electrophore sis and crosslinking revealed the complex formation between caldesmon and three EF-hand Ca-binding proteins, whereas calcimedin did not inte ract with caldesmon. In the presence of Ca2+, calcimedin binds to acti n-tropomyosin without affecting the interaction of caldesmon with this complex. Although calcimedin reversed the inhibitory action of caldes mon on the actomyosin ATPase activity at a lower concentration than th ree other Ca-binding proteins, this effect only slightly depends on Ca 2+ and was observed at the concentration of calcimedin comparable to t hat of actin. It is concluded that calcimedin itself cannot be respons ible for Ca-dependent regulation of caldesmon functioning, but actin b undling induced by calcimedin (or by other actin binding proteins) dec reases the inhibitory action of caldesmon on the actomyosin ATPase act ivity.