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

Biochemical Foundations of Human Vital Activity
Biochemistry of Proteins
Properties of Proteins

The manifestation of the biological activity of Proteins depends not only on their molecular Structure, but also on their chemical properties. The main PHYSICOCHEMICAL PROPERTIES OF Proteins include molecular weight, Water solubility, gel-forming capacity, Denaturation, amphotericity, buffering action, etc.

The Molecular Weight of proteins ranges from 6,000 to several million daltons. For instance, the molecular weight of the hormone Insulin is 5,733, Ribonuclease (an enzyme that degrades RNA) is 12,640, Myoglobin (a Muscle protein) is 17,000, Hemoglobin is 64,500, Blood serum globulin is 176,000, and Myosin (a muscle protein) is 493,000. The mass of protein molecules affects The rate of their movement in biological fluids.

The solubility of most proteins in water is due to their water-binding capacity: it increases at low concentrations of neutral salts and decreases at high concentrations. Aqueous protein solutions are colloids.

The ability to form gels or clots is of great physiological significance, as it imparts high elasticity or resilience to them (such as the proteins Collagen and Elastin, and the Actomyosin complex). Gels are structural assemblies of proteins (networks) in which the internal space is filled with a large amount of water.

Coagulation (from Lat. coagulatio — clotting, thickening) is the enlargement of particles in colloidal systems, which may be accompanied by The formation of a coagulant (a dense clot). Sometimes this leads to the formation of continuous volumetric structures (gelation).

Denaturation is the disruption of the native Cell/13.html">Protein Structure under METABOLISM/18.html">The Influence of various factors, leading to the loss of its biological activity (Fig. 89). Denaturation is observed upon heating, changes in medium pH, ultraviolet and ionizing radiation, mechanical impact, heavy metal salts, alcohol, and acetone. Upon rapid removal of the denaturing factors, the protein can return to its Native State (renature) with the restoration of its biological function.

The amphoteric Properties of Proteins are manifested due to the presence of free -NH₂ and -COOH groups. In an acidic environment, proteins can dissociate as bases, and in an alkaline environment, as acids. Upon interaction with acids and bases, proteins form salt-like compounds capable of precipitating. This principle underlies one of the Methods for Protein Isolation — precipitation by salting out. Protein amphotericity is utilized in separating them into individual fractions (Electrophoresis method) for the purpose of diagnosing various diseases and monitoring changes in functional states.

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Fig. 89 Diagram of protein molecule denaturation (unfolding) and its renaturation (return to the native state)

The buffering action of proteins (maintaining a constant pH in body Tissues) is characteristic of only a few proteins. These notably include hemoglobin, a potent intracellular buffer in erythrocytes, as well as certain Blood Plasma Proteins and the dipeptide carnosine.