Interaction of studies of a 100,000 dalton chymotryptic fragment of rabbit skeletal M-line protein with the S2 subfragment of myosin.

Controlled chymotryptic digestion of the 165,000 dalton component of the M-line of rabbit skeletal muscle, followed by Biogel P-150 chromatography of the digest, has led to the isolation of a homogeneous 100,000 dalton species. This fragment was found, by both sedimentation equilibrium and gel filtration chromatography, to interact with heavy meromyosin subfragment 2 (HMM-S2). The persistence of this fragment, after chymotryptic digestion, to bind HMM-S2, along with the known insensitivity of the M-line to proteolysis, suggests a structural role for the parent 165,000 dalton component along the lines of the M-filament, as suggested by the Knappeis and Carlsen model for M-line structure.