Human Biochemistry Volume 2 - Murray R. 1993
Biochemistry of Intracellular and Intercellular Communications
Pancreatic Hormones
Insulin-like Growth Factors
Although Insulin-like growth factors (IGF-1 and IGF-2) are not Pancreatic Hormones, they share a close Structural and functional resemblance to insulin. The effects of insulin on Cell growth and Replication are difficult to disentangle from the comparable effects of IGF-1 and IGF-2. Indeed, insulin and the insulin-like growth factors can act synergistically in this process. The structural similarities between these Proteins have already been noted (see also Fig. 51.8), and a more detailed comparison is presented in Table 51.5. IGF-1 and IGF-2 are single-chain Polypeptides consisting of 70 and 67 Amino Acids, respectively. The degree of Structure/154.html">Sequence Homology between these two hormones reaches 62%, with 50% of The amino acid residues in each being identical to those in insulin. The molecules of these growth factors possess distinct antigenic sites and are regulated differently (Table 51.5). Insulin exerts a more potent metabolic effect than the insulin-like growth factors, whereas the latter are more effective stimulators of cell growth. Each of these hormones binds to its own specific receptor. The IGF-1 receptor, much like the Insulin Receptor, is a heterodimer with an a2-ß2 subunit structure and exhibits Tyrosine kinase activity. The IGF-2 receptor consists of a single polypeptide chain with a Molecular Weight of 260,000 and lacks tyrosine kinase activity.
Class="center">Table 51.5. Comparison of Insulin and Insulin-Like Growth Factors
|
Insulin |
IGF-1 (Somatomedin C) |
IGF-2 (Multiplication-stimulating activity, MSA) |
|
|
Number of amino acid residues |
51 |
70 |
67 |
|
Source |
Pancreatic ß Cells |
Various tissues |
|
|
Regulating factors |
Glucose |
Unknown |
|
|
Plasma levels |
0.3–2 ng/mL |
Within the ng/mL range |
Within the ng/mL range |
|
Plasma binding protein |
None |
Present |
Present |
|
Primary physiological role |
Skeletal and Cartilage growth |
Unknown, potentially plays a role in embryonic development |
Fig. 51.18. Amino Acid Sequence of Glucagon. (Reproduced, with permission, from Katzung B.G. (ed.), Basic and Clinical Pharmacology, 3rd ed., Appleton and Lange, 1987.)
Table 51.6. Binding of Insulin, IGF-1, and IGF-2 to Various Receptors
|
Receptor |
|||
|
Hormone |
Insulin |
IGF-1 |
IGF-2 |
|
Insulin |
High |
Low |
Negligible |
|
IGF-1 |
Moderate |
High |
Moderate |
|
IGF-2 |
Negligible |
Low |
High |
These hormones are capable of cross-reacting to some extent with each other's receptors, which likely accounts for their overlapping biological activities (Table 51.6). As a rule, the growth-promoting potency of these hormones correlates best with their affinity for IGF-1 and IGF-2 receptors.
Last update: 06/08/2026
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