Biochemistry of muscular tissue

Muscular tissue consists of 80% of water and 20% of dry part. Dry part consists of 18-19% of organic compounds and 1-2% of inorganic compounds. Organic compounds are proteins and extractive substances. Proteins of muscles are divided into myofibrilar, sarcoplasmic, stroma’s and nucleoproteins. Extractive substances are divided into nitrogen-containing and nitrogenless substances. Nitrogenless substances are lipids, glycogen and products of their metabolism and creatine, creatinine, anserine, carnosine, adenylic system (ATP, ADP, AMP).

Anserine and carnosine take part in relaxation of muscles, maintain pH in muscles, antioxidants and activate ATP-ase’s activity of myosin.

Myofibrilar proteins make up 50-55% from all proteins of muscles. They’re divided into:

1) contractory (Myosin, actin, actomyosin, phosphorylated caldesmon in smooth muscles only)

2) relaxatory (titin, dephosphorylated caldesmon in smooth muscles only)

3) regulatory (tropomyosin (Tm), troponin (Tn), myosinbinding protein, alfa-actinin, nebulin

4) function of which is unknown (desmin, dystrophin)

Sarcoplasmic proteins make up 30-35% of total proteins of muscles. They’re divided into specific and non-specific. Specific proteins are myoglobin and calcineurin. Non-specific proteins are enzymes (e.g. aldolase), myoalbumins, myoglobulins.

Myoglobin consists of globin (1 chain from 153 amino acids) and heme like heme of hemoglobin. Myoglobin transfers oxygen in myocytes: Mgb + O2 ↔ MgbO2. Myoglobin is a storage of oxygen in muscles and pigment of them.

Stroma’s proteins are collagen and elastin (10% from all proteins of muscles) repeat, please, properties of these proteins, see theme 2 “Simple proteins”

Nucleoproteins repeat, please, composition of NP and formulas of heme, ATP, ADP, AMP, Creatine, Creatinine, Creatine phosphate, nucleotides

Chemical base of muscular contraction (schematically)

Nerve impulseàacetylcholineàcalcium release into synaptic spaceàcalcium enters the myocyteàcalcium binds with troponin which is constituent of triple complex – Tn-A-M, during this interaction Tn is released from this complex and interacts with tropomyosinàactin and Myosin forms an active complex named actomyosin under influence of potassiumàunder action of magnesium actomyosin complex cleaves ATP to ADP+inorganic phosphate, releasing energyà released energy is used for muscular contraction. Thus, the ATP supplying underlies the process of muscular contraction

The pathways of resynthesis of ATP (should be repeated calculation of ATP and formulas of creatine kinase)

1) creatine kinase’s reaction

2) glucose

3) TAG

4) ketone bodies

5) amino acids

6) crush-way: adenylylkinase’s reaction: 2ADP↔ATP + AMP

The peculiarities of contraction of smooth muscles

4Ca-calmodulinà dephosphorylated kinase of light chains of myosin à phosphorylated light chains of myosin à contraction

The relaxation of muscles

NO à cGMPà PKGàphosphorylated kinase of light chains of myosin (is inactive)à dephosphorylated light chains of myosinà relaxation

The peculiarities of myocardium

1) ketone bodies are main energetic source

2) creatine phosphate is a source of energy

3) aerobic glycolysis only