Myosin

Processed meats are heterogeneous systems composed of muscle itself and various nonmuscle ingredients including polysaccharides, flavor agents, salt, and phosphates. It is well established that proteins are largely responsible for the functional characteristics of muscle foods.

The most obvious structures within the muscle fiber are the myofibrils which are the units responsible for contraction and relaxation of the fiber.

The myofibrils contain 2 kinds of protein filaments:
a. Thick filaments –composed of myosin.
b. Thin filaments –composed of Actin, troponin and tropomyosin .

Myosin comprises about 45% of muscle protein. The founding members of the myosin superfamily are class 2 or conventional myosins. In mammals, there are 15 genes encoding myosin-2 heavy chains (MHC-2). They are among the most abundant proteins, as they constitute the primary contractile element in the sarcomeres of skeletal, smooth, and cardiac muscles.

Myosin-2 is formed of six polypeptide chains, two MHC-2, and two pairs of distinct light chains (LC). The architecture of this hexamer is highly asymmetric. Each MHC-2 consists of an N-terminal head region, which is the common element found in all members of the myosin family.
Myosin

Components of myofibrils

The most obvious structures within the muscle fiber are the myofibrils which are the units responsible for contraction and relaxation of the fiber.

Each myofibril consists of two sets of filaments: a thick set of filaments containing the protein myosin and thin set of filaments containing the protein actin. These two sets are arranged within the myofibril.

It is the light and dark bands of the myofibrils that give the muscle fiber its striated appearance. The dark, anisotropic, A-Bands correspond to the presence of myosin (thick) filaments, while the light, isotropic, I-bands contain the actin (thin) filaments.

In the center of the light I-band the line is called Z-line. Actin filaments are attached to these Z lines (or Z disc) and extend in both directions.

The thin filament (I bands) extend longitudinally from Z lines, which the thick filament (A band) span the gaps between the tips of the opposing actin units.

Components of myofibrils

Myofibrils of muscle fiber

Skeletal muscles vary in shape and size. The central portion of a whole muscle is called the belly. The belly comprises smaller compartments called fascicule.

Each fasciculus consists in turn of approximately 100 to 150 individual muscle fibers that range from 1 to 40 micrometers in length and 10 micrometers in dimeter.

A muscle fiber comprises a number of long, thin, cylindrical rods known as myofibrils, the essential contractile units of muscle, which are separated from one another by a highlight specialized network of tubules the sarcoplasmic reticulum.

The sarcoplasmic reticulum, a specialized organelle that’s stores and releases calcium, is an interconnecting network of tubules running parallel with and wrapped around the myofibrils.

The major significant of the sarcoplasmic reticulum is its ability to store, release and take up calcium and thereby control muscle contraction.

Myofibrils are bathed in an aqueous fluid (sarcoplasm), which is about 75-80% water and contains mitochondria, enzymes, glycogen, adenosine triphosphate, creatine, phosphate and myoglobin.

Myofibrils range in diameter from 1 to 2 micrometers. They are grouped in clusters and run the length of the muscle fiber. In turn each myofibril comprises long, thin strands of serially linked sarcomeres. Sarcomeres are the functional unit of a muscle.
Myofibrils of muscle fiber