Most globular proteins are denatured and lose their activity when briefly heated to 65°C. However, globular proteins that contain multiple disulfide bonds often must be heated longer at higher temperatures to denature them. One such protein is bovine pancreatic trypsin inhibitor (BPTI), which has 58 amino acid residues in a single chain and contains three disulfide bonds. On cooling a solution of denatured BPTI, the activity of the protein is restored. What is the molecular basis for this property?
Added by Judy N.
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Globular proteins are denatured when heated, which means they lose their native structure and function. Show more…
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Globular proteins are typically constructed from several layers of secondary structures, with a hydrophobic core and a hydrophilic surface. Is this true for fibrous proteins such as keratin? Explain. You are performing site-directed mutagenesis to test predictions about which residues are essential for protein function. Which of each pair of amino acid substitutions listed below would you expect to disrupt protein structure the most? Explain. Val replaced by Ala or Phe. Lys replaced by Asp or Arg. Gln replaced by Glu or Asn. Pro replaced by His or Gly. Protein denaturation can be triggered by a variety of environmental insults, including high temperature, covalent modification, and oxidation. Explain why researchers have observed a correlation between the level of heat shock proteins and the ratio of oxidized to reduced glutathione in cells subjected to oxidative stress.
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When a native protein in solution is heated to a high enough temperature, its polypeptide chain will unfold to become the denatured protein. The temperature at which a large portion of the protein unfolds is called the melting temperature. The melting temperature of a certain protein is found to be $46^{\circ} \mathrm{C}$, and the enthalpy of denaturation is $382 \mathrm{kJ} / \mathrm{mol}$. Estimate the entropy of denaturation, assuming that the denaturation is a two-state process; that is, native protein $\longrightarrow$ denatured protein. The single polypeptide protein chain has 122 amino acids. Calculate the entropy of denaturation per amino acid. Comment on your result.
Denaturation and Hydrolysis Simply put, denaturation means unfolding. Previous pages have discussed the factors that stabilize the shape of a protein, with all its helices, loops, and folds. If those stabilizing factors are disrupted, the protein falls out of shape. Even though its amino acids (primary structure) remain linked, without its correct secondary and tertiary structure the denatured protein can no longer function. For example, the body's enzymes lose their ability to catalyze the needed chemical reactions, if our body temperature changes too drastically. (Denatured proteins sometimes taste better though! People who eat eggs often prefer them cooked – denatured by heat. In ceviche, the seafood proteins are "cooked" by denaturing them with lime juice, which is acidic.) List the six causes of protein denaturation:
Riaz A.
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