Isolation of calelectrin-like proteins associated with smooth muscle plasma membranes

Plasma membranes prepared from pig stomach smooth muscle (antral part) were extracted with Triton X-100 to isolate insoluble cytoskeletal components. Reextraction of the insoluble material in EGTA yielded a protein complex which resembled the family of proteins that has been designated as 'mammalian calelectrins' [Südhof, T.C. et al. (1984) Biochemistry 23, 1103-1109]. Plasma membranes prepared in the presence and in the absence of 0.6 M KCl differed by the amount of these proteins, but in both preparations the EGTA-extractable proteins were quantitatively important constituents. Two of these proteins were further purified by means of ion exchange chromatography to apparent homogeneity as judged from sodium dodecyl sulfate gel electrophoresis.