Hon

mwmmm

57 kDa

12.5 kDa m

57 kDa 12.5 kDa

Miiilerian inhibiting substance (MIS)

FIGURE 19-9 Structural relationships between members of the transforming growth factor-/3 (TGF-/3) family. TGF-/3,_3 are homodi-mers with different subunits. The homology between the subunits is greater than 80%. The a-subunits of inhibins and activins are unlike any other structures in the TGF-/3 family. The /3-subunits of inhibin A and inhibin B (designated /3A and f}B) are approximately 30% homologous to TGF-/3 subunits. The activins consist of either homodimers or heterodimers of the /3A and / or /3B-subunits. Members of this family were isolated from intact cells and tissues as larger prohormones, which, in the case of the three patriarchal TGF-/3's, remain inactive until the mature dimers shown are liberated from their latent form by exposure to acidic conditions or proteases. An exception to this is the Miiilerian inhibiting substance (MIS), which was isolated as a much larger active dimer, each element of which is 70 kDa. The smaller homodimer, consisting of identical 12.5-Da subunits, is cleaved from the precursor by plasmin digestion and found to retain the same biological activity as the larger form of MIS. Reproduced with permission from Russell, W. E., and Van Wyk, J. J. (1995). Peptide growth factors. In "Endocrinology" (L. ]., DeGroot, ed.), 3rd ed., Vol. 1, pp. 2590-3623. W.B. Saunders Co., Philadelphia, PA.

also a factor that prevents the death of motor neurons. CNTF seems to belong to a family of hematopoietic cytokines, as shown in Figure 19-12. These cytokines include granulocyte colony-stimulating factor (G-CSF), oncostatin M (OSM), leukemia inhibitory factor (LIF), and interleukin (II-6).

A-Chain (7q11) AA

0 0

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