Question

ATPase activity in muscle fibre lies with

• A. Light meromyosin
• B. Head of heavy meromyosin
• C. Troponin
• D. Short arm of heavy meromyosin

Answer 1

The correct option is B Head of heavy meromyosin

• The myofibril is composed of two types of filaments. They are thick filament(Myosin) and Thin filament(Actin).
  
• Increase in Ca++ level leads to the binding of calcium with a subunit of troponin i.e troponin-C on actin filaments and thereby remove the masking of active sites for myosin. Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
  
• Each myosin (thick) filament is also a polymerized protein. Many monomeric proteins called Meromyosins constitute one thick filament. Each meromyosin has the globular head which is an active ATPase enzyme and has binding sites for ATP and active sites for actin. Hence ATPase activity in muscle fibre lies with Head of heavy meromyosin.
• So, the correct answer is 'Head of heavy meromyosin'.