Answer: The diagram (left) shows the structure of the

Chapter 25, Problem 25.51

(choose chapter or problem)

The diagram (left) shows the structure of the enzyme ribonuclease in its native form. The three- dimensional protein structure is maintained in part by the disulfide bonds (SS) between the amino acid residues (each color sphere represents an S atom). Using certain denaturants, the compact structure is destroyed and the disulfide bonds are converted to sulfhydryl groups (SH) shown on the right of the arrow. (a) Describe the bonding scheme in the disulfide bond in terms of hybridization. (b) Which amino acid in Table 25.2 contains the SH group? (c) Predict the signs of DH and DS for the denaturation process. If denaturation is induced by a change in temperature, show why a rise in temperature would favor denaturation. (d) The sulfhydryl groups can be oxidized (that is, removing the H atoms) to form the disulfide bonds. If the formation of the disulfide bonds is totally random between any two SH groups, what is the fraction of the regenerated protein structures that corresponds to the native form? (e) An effective remedy to deodorize a dog that has been sprayed by a skunk is to rub the affected areas with a solution of an oxidizing agent such as hydrogen peroxide. What is the chemical basis for this action? (Hint: An odiferous component of a skunks secretion is 2-butene-1-thiol, CH3CHCHCH2SH.2 H H H H H H H H Native form Denatured form