. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RECURRING THEMES AND VARIATIONS 145 External Environment Ex tracellular Membrane. Intracellular <—W V Theme Variations: 1. External environment 2. Receptor binding site 3. G-protem 4. Second messenger enzyme 5. Other Figure 2. A recurring theme for transmembrane signaling: generalized structure of a G protein-coupled system. Binding of an extracellular ligand activates the receptor which is coupled to a dissociable G protein (G) that links receptor activation to a cascade of subsequent transduction components depicted as:
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RECURRING THEMES AND VARIATIONS 145 External Environment Ex tracellular Membrane. Intracellular <—W V Theme Variations: 1. External environment 2. Receptor binding site 3. G-protem 4. Second messenger enzyme 5. Other Figure 2. A recurring theme for transmembrane signaling: generalized structure of a G protein-coupled system. Binding of an extracellular ligand activates the receptor which is coupled to a dissociable G protein (G) that links receptor activation to a cascade of subsequent transduction components depicted as: the second messenger enzyme, adenylate cyclase (AC); the second messenger. cAMP; and a protein kinase (PK) that phos- phorylates an ion channel. Examples of variations in the depicted theme include: (1) an external environment composed of seawater for a che- moreceptor of a marine organisms, or of the fluid in a synaptic cleft for an internal synaptic receptor; (2) a binding site affecting receptor acti- vation after binding specific ligands that may range from small cate- cholamines to a 28 kd glycoprotein hormone (Kobilka. 1992); (3) a dis- sociable G protein yielding a and fiy subunits which may stimulate or inhibit a second messenger enzyme, or directly affect an ion channel (, Birnbaumer. 1990; Simon etui., 1991). (4) other second messenger enzymes: , phospholipase C that yields diacylglycerol and inoshol trisphosphate (ibid: Berridge and Irvine. 1989). or phospholipase A2 yielding arachidonic acid and its metabolites (Shimizu and Wolfe, 1990; Simon et 1991). This latter system recurs in such disparate forms as the external chemoreceptors of sea urchin sperm and the in- ternal receptors for atrial natriuretic peptides in mammals and fish. In the next paper, Baldomero Olivera and colleagues reveal that cone snails produce families of small peptide venoms that cause debilitating effects by disrupting spe- cific, recurring transmembrane signaling systems of bo
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
