Each actin filaments is having two forms Monomer G-actin and polymeric F-actin.
G-actin is presence of `Mg^(++)` forms polymeric filamentous F-actin.
Tropomyosin also run close to the .F. actin throughout its length. br A complex protein troponin is distributed at regular intervals on the tropomyosin.
In a resting state a sub unit of troponin masks the active binding sites of myosin on the actin filaments.
(a) Troponin I `T_(p)I ("Inhibitor location")`
(b) Troponin T `T_(p)T ("Tropomyosin location")`
(c) Troponin C `T_(p)C (Ca^(++)" joining location")`
Each myosin filaments is formed of polymerised protein. They are present only in A disc
many monomeric proteins called Meromyosins constitute one tick filament.
Each meromyosins has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM).
The HMM component, i.e, the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and is known as cross arm.
The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.
