Question

Enzyme ATPase required for muscle contraction is located in
A. Actin
B. Troponin
C. Actiniin
D. Myosin

Answer 1

Hint:Skeletal muscle is made up of muscle cells, which in turn made up of muscle fibre. Each muscle fibre consists of thick myofilaments and thin myofilaments. Myofilaments are the filaments of myofibrils, constructed from proteins, principally myosin or actin.

Complete answer:
Each skeletal muscle consists of a large amount of muscle fibre. Each muscle fibre or muscle cell is composed of thin and thick myofilament having diameter 15nm and 7nm respectively. These thin and thick myofilaments are major contractile proteins. Thin myofilament is made up of actin protein whereas the thick myofilament is formed of myosin molecules.

Myosin is formed of six polypeptides chains out of which two are heavy chains and four are light chains. One end of each heavy chain is folded into a globular protein called myosin head and the elongated part is called the tail. The light chains are also part of heavy chain 2 in each heavy chain that helps in the contraction of muscles. myosin filament gets split up into two fragments by the enzyme trypsin called light meromyosin (LMM) and heavy meromyosin (HMM). LMM lacks ATPase enzyme whereas HMM is having ATPase enzyme. ATPase requires $Mg^{++}$. Myosin ATPase is an enzyme with ATP phosphohydrolase.

This enzyme act as a catalyst for catalysis the chemical reaction:
ATP + Water = ADP + phosphate. ATP on hydrolysis provides energy for the contraction of actin and myosin protein. Not only myosin but also ATPase enzyme acting as a site for action binding. Therefore by the above evidence, we came to know that myosin has ATPase enzyme.

Hence the correct answer is option ‘D’ i.e, myosin.

Note:Myosin protein which is part of thick myofilament is a primary contractile protein. After splitting of myosin into HMM and LMM. HMM, the area is having an active site of ATPase enzyme( a group of enzymes that catalyze the hydrolysis of a phosphate bond in adenosine triphosphate (ATP) to form adenosine diphosphate (ADP).