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730 Chapter 21
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76.
a. 1.
Tyr-Gly-Gly-Phe-Met-Thr-Ser-Gly-Lys
Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe-Lys-
Asn-Ala-Ile-Ile-Lys, Asn-Ala-Tyr-Lys, Lys, and Gly-Glu
2.
Tyr-Gly-Gly-Phe-Met
Thr-Ser-Gly-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe-Lys-Asn-Ala-Ile-Ile-Lys-Asn-Ala-
Tyr-Lys-Lys-Gly-Glu
3.
Tyr
Gly-Gly-Phe
Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe
Lys-Asn-Ala-Ile-Ile-Lys-Asn-Ala-Tyr
Lys-Lys-Gly-Glu
b.
N-terminal end: Tyr-Gly-Gly-Phe-Met
C-terminal end: Tyr-Lys-Lys-Gly-Glu or Tyr-Lys-Lys-Glu-Gly
77.
Because the native enzyme has four disulfide bridges, we know that the denatured enzyme has eight cys-
teine residues. The first cysteine has a one in seven chance of forming a disulfide bridge with the correct
cysteine. The first cysteine of the next pair has a one in five chance, and the first cysteine of the third pair
has a one in three chance.
1
7
*
1
5
*
1
3
=
0.0095
If disulfide bridge formation were entirely random, the recovered enzyme should have 0.95% of its origi-
nal activity. The fact that the enzyme the chemist recovered had 80% of its original activity supports his
hypothesis that disulfide bridges form after the minimum energy conformation of the protein has been
achieved. In other words, disulfide bridge formation is not random, but is determined by the tertiary struc-
ture of the protein.