Isolation and Physical Chemical Properties of an M-Line Protein from Skeletal Muscle

Abstract A procedure for the isolation of an M-line protein from chicken skeletal muscle is described. This includes the extraction of M-line protein with 5 mm Tris buffer (pH 7.7) and removal of contaminants by their precipitation at pH 5.0 followed by their absorption on DEAE-cellulose in 50 mm Tris buffer (pH 8.6). Identification of the M-line protein is based on the ability of antibody prepared against crude M-line extract to specifically alter the thickness and stability of the M-line structure in myofilament preparations. The isolated protein caused the aggregation of myosin filaments. The protein is a globular particle of low axial asymmetry and molecular weight 88,000 ± 2,000. It dissociates into two subunits of molecular weight 43,000 ± 1,000 in 6 m guanidine HCl. Evidence is presented showing a high degree of homogeneity with respect to size of the native protein in dilute salt solution as well as the subunit species under denaturing conditions.