IDENTIFICATION OF CASEIN KINASE-II AS A MAJOR ENDOGENEOUS CALDESMON KINASE IN SHEEP AORTA SMOOTH-MUSCLE

A caldesmon kinase activity was detected in an ATP extract of the myof ibril-like pellet from sheep aorta. The enzyme was purified 745-fold a nd was identified as casein kinase II on the basis of molecular size, substrate specificity, and high sensitivity to heparin inhibition. Cas ein kinase II phosphorylated isolated caldesmon and caldesmon incorpor ated into native thin filaments, and transferred about 1 mol of phosph ate per mol of caldesmon-h. Ser-73 was the main site phosphorylated by casein kinase II in chicken gizzard caldesmon. Phosphorylation of cal desmon reduced its affinity for smooth muscle myosin but had no effect upon the ability of caldesmon to inhibit the ATPase activity of actom yosin.