The thick filaments of the muscle has the protein mysoin. Each myosin molecule is made up of a monomer called meromyosin. It has a globular head, a short arm and a tail. The short arm constitutes the heavy meromyosin (HMM). The tail portion forms the light meromyosin (LMM). The head bears an actin-binding site and an ATPbinding site. It also contains ATPase enzyme that split ATP to generate energy for the contraction of muscle.
The thin filaments are composed of two intertwined actin molecules. It has polypeptide subunits called globular actin or G-actin and filamentous form or F-actin.
Each thin filament is made of two F-actins helically wound to each other. Each F-actin is a polymer of monomeric G-actins. Tropomyosin and troponin are other proteins which help in regulating the contraction of muscles along with actin and myosin.
