A specific substrate for protein kinase C (PKC) has been purified to apparent homogeneity from neuronal tissue of the honeybee Apis mellifera. The phosphoprotein shows an apparent molecular mass of 86 kDa, generates multiple spots around the pH of 4.6 upon isoelectric focussing and shows phosphopeptide patterns after limited proteolysis that are nearly identical to those of myristoylated alanine-rich C kinase substrate (MARCKS) purified from bovine brain. Investigations of the functional properties show, that the 86 kDa protein is regulated by both, the phosphorylation by PKC and by Ca2+/calmodulin. The phospho- and dephospho-86 kDa protein bind to F-actin with dissociation constants of K(d) approximately 280 nM and K(d) = 690 nM, respectively. Ca2+/calmodulin inhibits both, the phosphorylation of the 86 kDa protein by PKC and its interaction with F-actin. These data strongly suggest that the insect 86 kDa protein is a potential site of convergence of the Ca2+/calmodulin and PKC signalling pathways in the regulation of cytoskeleton-membrane rearrangement, with structural and functional homologies to vertebrate MARCKS.