Receptors sites for

Transport. Transcobalamin II dehvers the absorbed vitamin 3 2 to cells and is the primary plasma vitamin B22-binding transport protein. It is found in plasma, spinal fluid, semen, and extracellular fluid. Many cells, including the bone marrow, reticulocytes, and the placenta, contain surface receptor sites for the transcobalamin II—cobalamin complex. 

Cells possess surface receptor sites for the chemical messengers of the body. Should an autoantibody be produced against this site, it can combine with it and cause the same effect as the chemical messenger, e.g. thyrotoxicosis caused by autoantibody to the receptor site to TSH as previously described (section 4.10). 

Cannabinoid receptors are expressed throughout the cerebral cortex and the hippocampus, and a subpopulation of these cells appear to show an unusually high level of activity. It is possible that cells in these areas modulate the sensory effects of cannabis, particularly the effects on perception, task performance and memory. In addition, the anticonvulsant properties of cannabis are believed to be mediated here. Parts of the hypothalamus show high levels of receptor sites for cannabinoids this may be related to hypothermia effects. High levels in the cerebellum may be related to mediating the property of cannabinoids that produces the reduction in ataxic (muscle co-ordination) symptoms in certain disorders (Herkenham et al., 1991). 

Lovell, R. A., and Freedman, D. X. (1976) Stereospecific receptor sites for d-lysergic acid diethylamide in rat brain Effects of neurotransmitters, amine antagonists and other psychotropic drugs. Mol. Pharmacol., 12 620-630. 

Influenza virus particles are spheroidal and approximately 100 nm in diameter. The outer-membrane envelope contains 500 copies of hemagglutinin (HA) trimers and 100 copies of neuraminidase tetramers. The hemagglutinin constitutes the receptor sites for a-sialoside ligands. X-ray analyses show that the three sialic acid binding pockets reside 46 A apart, each trimer being separated on the virion surface by about 65-110 A [42],... 

Mosquitoes detect lactic acid, which is volatile, as a signal for the presence of an animal surface for feeding. A receptor site for lactic acid is present on the antennae of the mosquito. 

The Na" channel has a receptor site for cyclic GMP when cyclic GMP is bound, the channel is closed. This leads to a decrease in the intracellular Na ion concentration, resulting in hyperpolarisation of the cell membrane. This decreases the release of the neurotransmitter glutamate into the synapse that connects the photoreceptor cell to the bipolar neurones. In this specific case, a decrease in the neurotransmitter concentration in the synapse is a signal that results in depolarisation of the bipolar cell. The action potential in the bipolar cells communicate with ganglion cells, the axons of which form the optic nerve. Thus action potentials are generated in the axons which are... 

At the cellular level, plant secondary metabolites have five major effects on herbivores (a) alteration of DNA replication, RNA transcription, and protein synthesis (b) alteration of membrane transport processes (c) enzyme inhibition and activation (d) blocking of receptor sites for endogenous chemical transmitters and (e) affecting the conformation of other macromolecules (Robinson, 1979). 

Suggestion for conformation at the receptor site for pole-jumping activity... 

Combining different IMNs with common receptor sites enhances efficacy, low dosages avoid dose-dependent hematological adverse effects because of the different receptor sites for side effects and finally, cyclosporin (CyS) may block oxidation of MTX to its relatively inactive metabolite, 7-OH-MTX, thereby potentiating MTX efficacy. 

Vincent, J.P., Vignon, J., Kartalovski, B., and Lazdunski, M. Receptor sites for phencyclidine in mammalian brain and peripheral organs. In Domino, E.F., ed. PCP (Phencyclidine) Historical and Current Perspectives. Ann Arbor, MI. NPP Books. 1981. p. 83-103. 

That secretion of 2-acetamidoglucal, which is known to be an intermediate in the complex, 2-epimerase reaction, but cannot be isolated under normal conditions, may point to another defect in this enzyme that may be independent of the presence or absence of a feedback-inhibition receptor site for CMP-Neu5Ac has been discussed.233 An excess of 2-acetamidoglucal may be converted spontaneously into GlcNAc and this, enzymically, into ManNAc both compounds are secreted in the urine of the sialuria patient. As a consequence of these reactions, the cellular concentration of ManNAc may increase to a level leading to the synthesis of additional Neu5Ac from this compound by the action of acylneuraminate pyruvate-lyase. All of these reactions, and known or theoretical interactions, were summarized in Fig. 3 of Ref. 233. 

Receptor sites for angiotensin II, the main active peptide of the renin-angiotensin system, have been found in the ovaries (Lightman et al., 1989). Ovarian renin-angiotensin may also have an autocrine role in angiogenesis, steroidogenesis and oocyte maturation. Inhibin is produced by the ovarian follicle and corpus luteum (Tsonis et al.,... 

Scholtysik G, Quast U, Schaad A. Evidence for different receptor sites for the novel cardiotonic S-DPI201-106, ATX II, and veratridine at the cardiac sodium channel. Eur J Pharmacol 1986 125 111-118. 

Thomsen WJ, Catterall WA. Localization of the receptor site for a-scorpion toxins by antibody mapping implications for sodium channel topology. Proc Natl Acad Sci USA 1989 86 10161-10165. 

Catterall, W.A. and Striessnig, J. Receptor sites for Ca2+ channel antagonist, Trends Pharmacol. Sci. 1992, 13, 256-262. 

In addition to the multiplicity of receptor sites for glutamate, the NMDA receptors bear their own complexity as they are constructed as multimers from three distinguishable subunit classes (i.e. NR1, NR2 and NR3 subunit class). With regard to the stoichiometry of the NMDA receptor there is still some debate as to whether a native NMDA-gated ion channel within the cell membrane consists of either a tetramer or pentamer. More recently, it has been suggested that the tetramic stoichiometry is more probable (Laube et al., 1998 Hollmann, 1999). 

Long-term cocaine or amphetamine abuse leads to a deterioration of the nervous system. The body recognizes the excessive stimulatory actions produced by these drugs. To deal with the overstimulation, the body creates more depressant receptor sites for neurotransmitters that inhibit nerve transmission. A tolerance for the drugs therefore develops. Then, to receive the same stimulatory effect, the abuser is forced to increase the dose, which induces the body to create even more depressant receptor sites. The end result over the long term is that the abusers natural levels of dopamine and norepinephrine are insufficient to compensate for the excessive number of depressant sites. Lasting personality changes are thus often observed. 

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