Meromyosin

Meromyosin (mero meaning "part of") are subunits of the actin-associated motor protein, myosin formed by trypsin digestion (proteolysis). Following digestion, two types of meromyosin are formed: heavy meromyosin (HMM) and light meromyosin (LMM).

Light meromyosin has a long, straight portion in the “tail” region. Heavy meromyosin is a protein chain terminating in a globular head portion/cross bridge. 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.