296 Part III: Muscle Foods
continuity and strength of the muscle fibers. They
are soluble in high ionic strength buffers, and the
most important of them are listed in Table 13.2.
Myosin and actin are by far the most abundant and
form part of the structural backbone of the myofib-
ril. Tropomyosin and troponins C, T, and I are con-
sidered as regulatory proteins because they play an
important role in muscle contraction and relaxation
(Pearson 1987). There are many proteins in the Z-
line region (although in a low percentage) that serve
as bridges between the thin filaments of adjacent
sarcomeres. Titin and nebulin are two very largeTable 13.2.Type, Localization and Main Role of Major Muscle Proteins
Cellular
Localization Main Proteins Main Role in Muscle
Myofibril Myosin and actin Cytoskeletal proteins providing support to the myofibril
and responsible for contraction-relaxation of the
muscle
Tropomyosin Regulatory protein associated to troponins than cause its
movement towards the F actin helix to permit
contraction
Troponins T, C, I Regulatory proteins. Tn-T binds to tropomyosin, Tn-C
binds Ca^2 and initiates the contractile process and
Tn-I inhibits the actin-myosin interaction in conjunc-
tion with tropomyosin and Tn-T and Tn-C
Titin and nebulin Large proteins located between Z-lines and thin
filaments. They provide myofibrils with resistance and
elasticity
, , and eu-actinin Proteins regulating the physical state of actin. -actinin
acts as a cementing substance in the Z-line. -actinin
inhibits the polymerization of actin at the nucleation
step. -actinin is located at the free end of actin
filaments, preventing them from binding each other.
Eu-actinin interacts with both actin and -actinin
Filamin,synemin, Proteins located in the Z-line that contribute to its high
vinculin, zeugmatin, density
Z nin, C, H, X, F,
I proteins
Desmin Protein that links adjacent myofibrils through Z-lines
Myomesin, creatin Proteins located in the center of the sarcomere forming
kinase and M protein part of the M-line
Sarcoplasm Mitochondrial enzymes Enzymes involved in the respiratory chain
Lysosomal enzymes Digestive hydrolases very active at acid pH (cathepsins,
lipase, phospholipase, peptidases, glucohydrolases,
etc.)
Other cytosolic enzymes Neutral proteases, lipases, glucohydrolases, ATP-ases,
etc.
Myoglobin Natural pigment of meat
Hemoglobin Protein present from remaining blood within the muscle
Connective tissue Collagen Protein giving support, strength and shape to the fibers
Elastin Protein that gives elasticity to tissues like capillaries,
nerves, tendons, etc.
Sources:From Bandman 1987, Pearson and Young 1989.