CHARACTERIZATION OF CHICKEN GIZZARD CALCYCLIN AND EXAMINATION OF ITS INTERACTION WITH CALDESMON

Using a procedure developed to purify calcyclin from mouse Ehrlich asc ites tumor cells calcyclin was purified from smooth muscle of chicken gizzard. Chicken gizzard calcyclin bound to phenyl-Sepharose in a calc ium dependent manner as did mouse EAT cells and rabbit lung calcyclin but appeared to be more acidic than its mammalian counterparts as reve aled by ion exchange chromatography on Mono Q. Chicken gizzard calcycl in bound Ca-45(2+) on nitrocellulose filters and exhibited a shift in electrophoretic mobility on urea-PAGE depending on Ca2+ concentration. Crosslinking experiments with BS3 showed that chicken gizzard calcycl in was able to form noncovalent dimers. As indicated by a decrease in maximum tryptophan fluorescence emission of caldesmon (about 14% at 1 : 1 molar ratio) and displacement of calmodulin from its complex with caldesmon, chicken gizzard calcyclin binds caldesmon. This binding was , however, much weaker than that of calmodulin and could not influence the interaction of caldesmon with actin. In consequence, calcyclin wa s unable to reverse the inhibitory effect of caldesmon on actin-activa ted Mg2+-ATPase activity of myosin in the presence of Ca2+.