Microinjection of antibodies to the calpactin I light chain in MDBK cells causes precipition of the cytoskeletal calpactin I complex without affecting the distribution of related proteins.

The calpactin I complex is composed of two heavy chain (39K) and two light chain (11K) subunits. The heavy chain is a member of a protein family that includes lipocortins, endonexin and chromobindins while the light chain is a member of the S100 family (7 distinct members are known). We have found that the kidney epithelial cell line MDBK expresses four members of the heavy chain family and two members of the light chain protein family. Antibodies to the light chain of calpactin I were found to cause the precipitation of injected antibody together with the associated heavy chain without apparent effect on the distribution of related proteins. This suggests a differential targeting of various members of the calpactin heavy and light chain families even within the same cell.