Assembly of smooth muscle myosin into side-polar filaments.

Abstract

The in vitro assembly of myosin purified from calf aorta muscle was studied by EM. Two types of filament are formed: short bipolar filaments similar to those formed from skeletal muscle myosin and longer side-polar filaments having cross bridges with a single polarity along the entire length of one side and the opposite polarity along the other side. Unlike the case with skeletal myosin filaments, antiparallel interactions between myosin molecules occur along the whole length of side-polar filaments. The side-polar structure may be related to the in vivo form of myosin in vertebrate smooth muscle.