The conformation (structure) of the peptide chainis ordered and unique for each protein. Under special conditions, a large number of bonds break, which stabilized the spatial structure of the compound molecule. As a result of the rupture, the whole molecule (or a significant part of it) takes the form of a disorderly coil. This process is called "denaturation." This change can be provoked by heating from sixty to eighty degrees. Thus, each molecule obtained as a result of the rupture may differ in conformation from the others.
Denaturation of proteins occurs under the influence ofany agents capable of destroying non-covalent bonds. This process can occur in alkaline or acidic conditions, on the surface of the phase separation, under the influence of certain organic compounds (phenols, alcohols and others). Denaturation of the protein can also occur under the influence of guanidine chloride or urea. These agents form weak bonds (hydrophobic, ionic, hydrogen) with the carbonyl or amino groups of the peptide backbone and with a number of groups of amino acid radicals, substituting for the protein self-hydrogen bonds within the molecules. As a result, there is a change in the secondary and tertiary structure.
Resistance to the action of denaturing agentsdepends primarily on the presence in the molecule of the protein compound of disulfide bonds. The trypsin inhibitor has three S-S bonds. Under condition of their reduction, protein denaturation occurs without other influences. If, afterwards, the compound is placed in conditions where the oxidation of SH-groups of cysteine and formation of disulfide bonds is carried out, the initial conformation will be restored. Moreover, the presence of even one disulfide bond substantially increases the stability in the spatial structure.
Denaturation of the protein is usually accompanied bya decrease in its solubility. At the same time, a precipitate is often formed. It appears in the form of a "coagulated protein". When the concentration of compounds in the solution is high, "coagulation" undergoes the entire solution, as, for example, when cooking chicken eggs. During denaturation, the protein loses its biological activity. This principle is based on the use of carbolic acid (an aqueous phenolic solution) as an antiseptic substance.
The instability of the spatial structure,high probability of destruction under the influence of various agents significantly complicate the isolation and study of protein. Certain problems are also created when using compounds in industry and medicine.
If protein denaturation was carried out bythe effect of high temperatures, then under slow cooling, under certain conditions, a process of renativation takes place-the restoration of the native (initial) conformation. This fact proves that the laying of the peptide chain occurs in accordance with the primary structure.
Formation of native conformation (the originallocation) is a spontaneous process. In other words, this arrangement corresponds to the minimum amount of free energy enclosed in the molecule. As a result, it can be concluded that the spatial structure of the compound is encoded in the amino acid sequence in peptide chains. This, in turn, means that all polypeptides similar in amino acid sequence (eg, myoglobin peptide chains) will take an identical conformation.
Proteins can have significant differences in the primary structure, even if they are practically or absolutely identical in conformation.
