Biochemical effector systems

Carrero I, Femandez-Moreno MD, Perez-Albarsanz MA, et al. 1989. Lindane effect upon the vasoactive intestinal peptide receptor-effector system in rat enterocytes. Biochem Biophys Res Comm 159(3) 1391-1396. 

The action of a hormone is defined as the primary effect on a cell, usually the binding of the hormone to a specific receptor and the resultant interaction between the hormone-receptor complex and an effector system within the cell. The effect of a hormone is an experimental observation that is made either in vitro or in vivo it can be molecular, biochemical or physiological but, when a sufficient number of effects are established, a relationship between the action and effects can be drawn. This can best be described as a pyramid (Figure 12.2). The. function of a hormone is an... 

Figure 12.16 Multiple sites of hormone effects on the same biochemical process. The hormone binds to its receptor activating the effector system which increases the activity of two separate reactions in the same biochemical pathway (process) to increase flux through the pathway. This means that the flux can change without large changes in the concentrations of intermediates in the pathway, i.e. activation of E and E4 ensures increased flux from S to the product P with little change in the concentrab ons of A, B or C.

Zgombick JM, Beck SG, Mahle CD, Craddock-Royal B, Maayani S. Pertussis toxin-sensitive guanine nucleotide-binding protein(s) couple adenosine A, and 5-hydroxytryptamine1A receptors to the same effector systems in rat hippocampus biochemical and electrophysiological studies. Mol Pharmacol 1989 35 484-494. 

Adrenoceptors are proteins embedded in the cell membrane that are coupled through a G-protein to effector mechanisms that translate conformational changes caused by activation of the receptor into a biochemical event within the cell. All of the )3-adrenoceptors are coupled through specific G-proteins (Gg) to the activation of adenylyl cyclase (45). When the receptor is stimulated by an agonist, adenylyl cyclase is activated to catalyze conversion of ATP to cyclic-adenosine monophosphate (cAMP), which diffuses through the cell for at least short distances to modulate biochemical events remote from the synaptic cleft. Modu-lationof biochemical events by cAMP includes a phosphorylation cascade of other proteins. cAMP is rapidly deactivated by hydrolysis of the phosphodiester bond by the enzyme phosphodiesterase. The a,-receptor may use more than one effector system, depending on the location of the receptor however, to date the best understood effector system of the a,-receptor appears to be similar to that of the )3-re-... 

Abdallah, E.A., Jett, D.A., Eldefrawi, M.E., and Eldefrawi, A.T., Differential effects of paraoxon on the M3 muscarinic receptor and its effector system in rat submaxUlary gland cells, J. Biochem. Toxicol, 7, 125, 1992. 

The mechanism of promotion is subject to scientific research and considerable conjecture. The probability of multiple mechanisms is strong. A sequence of steps may be involved, leading to proliferation and differentiation. A parallel example might be the prostaglandin and cyclic nucleotide membrane effector systems. An early biochemical indicator of promotion is the induction of ornithine decarboxylase (ODC), and its presence has been used to discover new promoters. Increased levels of ODC appear to be associated with increased liver cell proliferation and might be related to the mechanisms of the promotion. ... 

The transduction pathways and effector systems that underlie the various physiological actions of adenosine remain to be defined. The intent of this article is to provide a discussion of our attempts to understand more fully the biochemical and functional consequences of Ai adenosine receptor mechanisms in the heart. 

Molybdate is also known as an inhibitor of the important enzyme ATP sulfurylase where ATP is adenosine triphosphate, which activates sulfate for participation in biosynthetic pathways (56). The tetrahedral molybdate dianion, MoO , substitutes for the tetrahedral sulfate dianion, SO , and leads to futile cycling of the enzyme and total inhibition of sulfate activation. Molybdate is also a co-effector in the receptor for steroids (qv) in mammalian systems, a biochemical finding that may also have physiological implications (57). 

Figu re 3.7. Theoretical model to illustrate the effect of biochemical cascades on dose-effect relationships. a A simple model cascade, containing an agonist (L), a receptor (R), a second messenger (M2), and an effector (E). b Equations derived from the assumptions in a. ECjq Ligand concentration required for the half-maximal effect. The effect will saturate at concentrations lower than those required for receptor saturation. The gap between K and ECjq depends on the number of receptors and other properties of the system, c Illustration of the equations stated inb. 

---