MOLECULAR SHAPE OF PROTEINS: PRIMARY, SECONDARY AND TERTIARY STRUCTURES
507
in the blood, severe acidosis, coma, and death. Treatment for diabetes requires daily injections of insulin; since
insulin is a peptide, it would be degraded by stomach acid if taken orally. Insulin does not cure the disease, so
treatment is lifelong.
Human insulin is composed of two straight-chain polypeptides joined by disulfide bridges.
Gly–Ile–Val–Glu–Gln–Cys–Cys–Thr–Ser–Ile–Cys–Ser–Leu–Tyr–Gln–Leu–Glu–Asn–Tyr–Cys– Asn
Phe–Val–Asn–Gln–His–Leu–Cys–Gly–Ser–His–Leu–Val–Glu–Ala–Leu–Tyr–Leu–Val–Cys–Gly–Glu– Arg–Gly–Phe–Phe–Tyr–Pro–Lys–Thr
A chain
B chain
10
9
8
29
28
21
30
human insulin
This structure is known to arise from a single straight-chain polypeptide, preproinsulin, containing 100 amino
acid residues. This loses a 16-residue portion of its chain and forms proinsulin, in which disulfide bridges connect
the terminal portions of the chain in a loop. A central portion of the loop (the C chain) is then cleaved out,
leaving the A chain (21 residues) bonded to the B chain (30 residues) by two disulfide bridges. There is also a
third disulfide bridge interconnecting two cysteine residues in the A chain. This is the resultant insulin.
SH HS
SH HS
SH
SH
16 residues
30 residues
21 residues
33 residues
B
A
C
S S
S S
S
S
B
A
C
S S
S S
S
S
B
A
preproinsulin
proinsulin
insulin
Mammalian insulins from different sources are very similar and may be used to treat diabetes. The compounds
show variations in the sequence of amino acid residues 8–10 in chain A, and at amino acid 30 in chain B.
insulin (human)
8
9
10
30
A chain
B chain
insulin (porcine)
insulin (bovine)
Thr Ser Ile
Thr
Thr Ser Ile
Ala
Ala Ser Val
Ala
28 29
Pro Lys
Pro Lys
Pro Lys
amino acid residues
Porcine insulin and bovine insulin for drug use are extracted from the pancreas of pigs and cattle respectively.
More frequently, human insulin is now employed. This is produced by the use of recombinant DNA technology
to obtain the two polypeptide chains, and then linking these chemically to form the disulfide bridges
507
in the blood, severe acidosis, coma, and death. Treatment for diabetes requires daily injections of insulin; since
insulin is a peptide, it would be degraded by stomach acid if taken orally. Insulin does not cure the disease, so
treatment is lifelong.
Human insulin is composed of two straight-chain polypeptides joined by disulfide bridges.
Gly–Ile–Val–Glu–Gln–Cys–Cys–Thr–Ser–Ile–Cys–Ser–Leu–Tyr–Gln–Leu–Glu–Asn–Tyr–Cys– Asn
Phe–Val–Asn–Gln–His–Leu–Cys–Gly–Ser–His–Leu–Val–Glu–Ala–Leu–Tyr–Leu–Val–Cys–Gly–Glu– Arg–Gly–Phe–Phe–Tyr–Pro–Lys–Thr
A chain
B chain
10
9
8
29
28
21
30
human insulin
This structure is known to arise from a single straight-chain polypeptide, preproinsulin, containing 100 amino
acid residues. This loses a 16-residue portion of its chain and forms proinsulin, in which disulfide bridges connect
the terminal portions of the chain in a loop. A central portion of the loop (the C chain) is then cleaved out,
leaving the A chain (21 residues) bonded to the B chain (30 residues) by two disulfide bridges. There is also a
third disulfide bridge interconnecting two cysteine residues in the A chain. This is the resultant insulin.
SH HS
SH HS
SH
SH
16 residues
30 residues
21 residues
33 residues
B
A
C
S S
S S
S
S
B
A
C
S S
S S
S
S
B
A
preproinsulin
proinsulin
insulin
Mammalian insulins from different sources are very similar and may be used to treat diabetes. The compounds
show variations in the sequence of amino acid residues 8–10 in chain A, and at amino acid 30 in chain B.
insulin (human)
8
9
10
30
A chain
B chain
insulin (porcine)
insulin (bovine)
Thr Ser Ile
Thr
Thr Ser Ile
Ala
Ala Ser Val
Ala
28 29
Pro Lys
Pro Lys
Pro Lys
amino acid residues
Porcine insulin and bovine insulin for drug use are extracted from the pancreas of pigs and cattle respectively.
More frequently, human insulin is now employed. This is produced by the use of recombinant DNA technology
to obtain the two polypeptide chains, and then linking these chemically to form the disulfide bridges