[Localization of segments, phosphorylated by Ca-phospolipid-dependent protein kinase in smooth muscle caldesmon]

Phosphorylation of caldesmon from duck gizzard by Ca-phospholipid-dependent protein kinase was investigated. Ca-phospholipid-dependent protein kinase transfers about 3.5 moles of phosphate per mole of caldesmon (140 kDa). Tropomyosin does not affect, while calmodulin strongly inhibits the phosphorylation of caldesmon by Ca-phospholipid-dependent protein kinase. Data from one-dimensional peptide mapping suggest that the sites phosphorylated by the enzyme are located in fragments with apparent molecular weights of 43 and 35 kDa, which are supposed to be located in the vicinity of N- or C-termini of the protein molecule and involved in the caldesmon interaction with actin and calmodulin.