Localization of three fragments of connectin in chicken breast muscle sarcomeres.

Connectin (titin) links the Z line to the myosin filament in sarcomeres of vertebrate skeletal muscle. An 800 kDa fragment of alpha-connectin runs from the Z line up to the N2 line region in the I band, and the following beta-connectin portion runs up to the edge of the M line on the myosin filament in chicken breast muscle sarcomeres. Immunoelectron microscopy showed that a 400 kDa fragment following the 800 kDa fragment reaches the edge of the myosin filament and, thereafter a 1,700 kDa fragment runs to the M line on the myosin filament in chicken breast muscle sarcomeres. When stretched, the epitopes to anti-400 kDa fragment antibodies outside the myosin filament moved toward the inside of the I band.