Structure of Myosin
Myosin is a large asymmetric molecule, it has a long
tail and two globular heads (Fig. M1).
The tail is about 1,600 Å long and 20 Å wide. Each head is about 165 Å long, 65 Å wide and 40 Å deep at its thickest part. The
molecular weight of myosin is about 500,000.
In strong denaturing solutions, such as 5 M guanidine-HCl or 8 M urea, myosin dissociates into six polypeptide
chains: two heavy chains (molecular
weight of each heavy chain about 200,000) and four light chains (two with a molecular weight of 20,000, one with 15,000 and
another with 25,000). The two heavy
chains are wound around each other to form a double helical structure. At one end both chains are folded into separate globular
structures to form the two heads. In the
muscle, the long tail portion forms the backbone of the thick filament and the heads protrude as crossbridges toward the thin
filament. Each head contains two light
chains.