63 67 73

63 67 73

FIGURE 15-12 Endothelins. Amino sequence of human endothelin isoforms and their respective proendo-thelins. The filled circles for ET-2 and ET-3 represent amino acid differences compared to ET-1 and its pro form. The arrow indicates the site of proteolytic cleavage by the endothelin-converting enzyme (ECE), which generates the mature, biologically active endothelins. The two solid lines indicate disulfide linkages. Also shown is the structure of the structurally homologous sarafotoxin b, which is present in the venom of the Egyptian asp Atractaspesis engaddensis. Adapted with permission from Rubanyi, G. M., and Bothelo, L. H. (1991). Endothelins. FASEB J. 5, 2713-2720.

toxin-insensitive G protein in all tissues expressing the ETa or ETb forms. This results in the production of IP3 and the mobilization of intracellular free Ca2+, leading to a transient increase in [Ca2+]j. Associated with these changes are the elevation of diaclyglycerol (DAG), activation of protein kinase C (PKC), and opening of a Ca2' channel. Then, as diagrammed in Figure 15-14,

TABLE 15-8 Properties of Endothelin Receptors

Receptor class

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