Meromyosin

Meromyosin is the monomeric unit , polymerised to form myosin (Derived from an Ancient Greek word méros). With regards to human anatomy myosin (Thick filament in muscle fibre) and actin (Thin filament in muscle fibre) constitute the basic functional unit of a muscle fiber, called sarcomere, playing role in muscle contraction as well as muscle relaxation.

Biochemically viewed meromyosin form subunits of the actin-associated motor protein, myosin, as commonly obtained by trypsin proteolysis (protein breakdown).^[1] Meromyosin consists ofthree different parts , The globular head, The tail, The short arm. Following this proteolysis, two types of meromyosin are formed: heavy meromyosin (HMM) and light meromyosin (LMM).^[2]

Light meromyosin has a long, straight portion called the “tail” region. Heavy meromyosin (HMM) is a protein chain terminating into a globular head portion and a short arm portion /cross bridge.^[3] HMM consists of two subunits, Heavy Meromyosin Subunit 1 and 2 (HMMS-1 and HMMS-2). The majority of myosin activity is concentrated in HMMS-1. HMMS-1 has an actin binding site and ATP binding site (myosin ATPase) that determines the rate of muscle contraction when muscle is stretched.

Light and heavy meromyosin are subunits of myosin filaments (thick myofilaments).

References

1. "meromyosin". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 8 October 2024.
2. Szent-Györgyi AG (1953). "Meromyosins, the subunits of myosin". Archives of Biochemistry and Biophysics. 42 (2): 305–320. doi:10.1016/0003-9861(53)90360-9. PMID 13031633.
3. Wendt T, Taylor D, Trybus KM, Taylor K (April 2001). "Three-dimensional image reconstruction of dephosphorylated smooth muscle heavy meromyosin reveals asymmetry in the interaction between myosin heads and placement of subfragment 2". Proceedings of the National Academy of Sciences of the United States of America. 98 (8): 4361–4366. Bibcode:2001PNAS...98.4361W. doi:10.1073/pnas.071051098. PMC 31840. PMID 11287639.