Biochemical Foundations of Human Vital Activity - Volkov, N. I., & Nesen, E. N. 2000

Biochemical Foundations of Human Vital Activity
Biochemistry of Proteins
Protein Metabolism during Muscular Activity

Proteins make a minor contribution to the METABOLISM/26.html">Energy Metabolism of muscular activity, accounting for only 10—15% of the body's total energy consumption. Nevertheless, they play a vital role in supporting the contractile function of skeletal Muscles and The Heart, shaping long-term adaptation to Physical Exercise, and establishing a specific compositional profile of muscles.

Physical exertion induces changes in protein Synthesis and degradation processes within Tissues, particularly in skeletal muscles and the Liver. The extent of these changes depends on the intensity and duration of the exercise, as well as the individual's fitness level. Alterations in intra-tissue Protein metabolism are typically assessed by measuring the Blood concentration of specific Essential Amino Acids, which are not synthesized by the body and are instead released during The breakdown of tissue proteins. 3-Methylhistidine is used as a specific marker for the degradation of the contractile proteins Actin and Myosin.

A single bout of exercise suppresses Protein Synthesis while enhancing Catabolism. For example, during one hour of treadmill running, The rate of Protein synthesis in the liver decreased by 20%, and during maximal exertion, by as much as 65%. A similar pattern is observed in skeletal muscles. Physical activity accelerates the breakdown of Muscle Proteins (predominantly structural ones), although certain types of exercise also increase the degradation of contractile proteins.

Systematic physical training activates adaptive protein synthesis in muscles and other tissues, increasing the content of structural and contractile proteins, as well as Myoglobin and numerous Enzymes. This leads to an increase in muscle mass and the cross-sectional area of muscle fibers, a phenomenon known as muscle hypertrophy. The increased quantity of enzymes creates favorable conditions for expanding the energy potential in working muscles, which in turn enhances The Biosynthesis of muscle proteins following exercise and improves human motor performance.

Speed and strength training predominantly stimulate the synthesis of myofibrillar proteins in muscles, whereas endurance training enhances the synthesis of mitochondrial enzymes responsible for aerobic ATP production. The type of physical activity (e.g., swimming, running) also largely determines the magnitude of changes in protein synthesis.

Adaptive changes in protein metabolism during muscular activity have been studied by A.A. Viru, V.A. Rogozkin, N.N. Yakovlev, and other researchers. They concluded that training induces an adaptive activation of all key Stages of Protein Synthesis in skeletal muscles, resulting in an overall increase in cellular protein-synthesizing capacity. Hormones such as glucocorticoids, adrenaline, somatotropin, thyroxine, and Insulin play a crucial role in inducing adaptive protein synthesis during training. They participate in facilitating the transition from acute adaptive responses to long-term adaptation.

N.N. Yakovlev summarized the potential pathways of adaptive protein synthesis in muscles under The Influence of systematic muscular activity (Fig. 100). The onset of biochemical adaptation is associated with increased activity of certain enzymes and a higher concentration of energy substrates. Enhanced energy metabolism leads to The formation of metabolites that act as Inducers of protein synthesis at the genetic level. Such inducers may include ADP, AMP, creatine, Certain amino acids, cyclic AMP, etc. Upregulation of The Genome activity enhances translation processes or the synthesis of structural, contractile, or enzymatic proteins, which, in turn, ensures the high functional performance of muscles in a trained Organism during muscular work.

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Fig. 100 Diagram of enhanced adaptive protein synthesis in muscles induced by systematic muscular activity

Amino acids—the breakdown products of endogenous proteins—make a significant contribution to the Energy supply of muscular activity, especially prolonged exercise. Their concentration in tissues during sustained physical work can increase 20- to 25-fold. These Amino acids are oxidized to replenish ATP or are channeled into Gluconeogenesis, helping to maintain blood glucose levels as well as Glycogen stores in The Liver and skeletal muscles (see Fig. 98).

Protein degradation and amino acid oxidation during muscular activity are accompanied by an accelerated production of ammonia (NH₃), which is bound in the liver via The Urea Cycle and excreted from the body. Consequently, physical exertion leads to elevated blood urea levels, and the normalization of these levels during the rest period indicates the recovery of protein breakdown and synthesis processes in tissues.

Review Questions

1. What is the protein content in The Human Body and what is the daily dietary intake?

2. Characterize The chemical composition, Structure, and Properties of Proteins.

3. What biological Functions do proteins perform in the body?

4. Describe the characteristics of Amino Acids and biogenic amines. What is The Role of creatine in the body?

5. Which amino acids are classified as dispensable (non-essential) and indispensable (essential)? How do they affect the Biological value of dietary proteins?

6. What chemical bond is known as a peptide bond? Write the reaction for the formation of a dipeptide.

7. What is meant by the primary, secondary, tertiary, and quaternary structures of proteins? What is their biological significance?

8. What properties are characteristic of proteins? How do these properties influence Protein Functions?

9. What are the Structural Features of muscle contractile proteins, Connective Tissue proteins, and oxygen carriers?

10. What tissue Peptides do you know? What is their role in the body?

11. Characterize the MAIN STAGES OF protein metabolism.

12. What is meant by nitrogen balance? How is the state of protein metabolism assessed?

13. What are the Specific features of protein breakdown during Digestion and the absorption of their Hydrolysis products?

14. Provide a general description of Protein Biosynthesis and its regulation.

15. Name the Main reactions of Amino acid metabolism in tissues. What is their significance for the organism?

16. How does the binding and Excretion of ammonia occur in the body? Explain The Essence of the urea cycle.

17. What are the patterns of changes in protein metabolism during muscular activity?