PROPERTIES OF MONOCLONAL-ANTIBODIES TO PLANT CALMODULIN

Ca2+-binding proteins link changes in cytoplasmic free Ca2+ concentration to physiological effects. Two monoclonal antibodies raised against purified calmodulin, the best documented such protein plants, bound plant calmodulin in enzyme-linked immunoassays and immunoprecipitation. Only one antibody recognised sodium dodecyl sulphate-denatured plant calmodulin while mammalian calmodulin was recognised with substantially lower efficiency. Immunoblotting crude extracts from a variety of angiosperms revealed two bands of similar M(r) that showed Ca2+-dependent mobility shifts on sodium dodecyl sulphate gel electrophoresis. Carboxypeptidase B digestion increased the proportion of the slowly moving band consistent with it being calmodulin from which the C-terminal lysine residue had been removed. The reaction may occur in vivo since both forms. but not a presumed proteolytic fragment of lower M(r), are detected when tissues are extracted directly into trichloroacetic acid to inhibit post-homogenisation proteolysis.