Amino dose-response

The prevalent receptor model for the excitatory amino acid is a tetrameric complex. As mentioned in the text, there is evidence that the channel conductance depends on the number of subunits that bind a ligand. Estimate the EC50 value and Hill coefficient for a dose-response curve assuming that the occupation at each subunit has a Kd value of 1 pi I, an % of 1, and that activation induces a transition to an active state independent of the state of the other subunits ... 

The first step in these studies has been the search for the shortest fragment of the ACTH chain that is essential for (maintenance of) activity. Next, changes in the peptide backbone and modification of the side-chains of the amino acid residues have been studied. As a test system the delay of extinction of an active avoidance response in rats as measured in a pole-jumping test after subcutaneous administration has been used (7 ) this assay method gives a graded dose-response relationship which allows the estimation of an ED50 and thus potency ratio s. The heptapeptide ACTH--(4-10) has been used as the reference peptide (8 ). For a more extensive review see ref. 9. 

This method can be used to compensate for inhibition of a biochemical pathway which results in a deficiency of an essential metabolic product. Detailed variations of the method are provided by Dayan et al.7 and Amagasa et al.1 The inhibitor concentration should be no higher than that required for strong herbicidal effect. Metabolite concentrations should be below that which is phytotoxic. For example, certain amino acids such at methionine, are growth inhibitors at relatively low concentrations. So, in preliminary work, dose-response studies should be done with amino acids to find the maximum concentrations that do not inhibit growth. Then, seeds of test plants should be imbibed in solutions of the phytotoxin with and without metabolite solutions. Amino acids, tricarboxylic acid cycle intermediates, vitamins, nucleotides, and reducing agents have all been used in complementation studies to elucidate modes of action of a variety of phytotoxins. Examples of each of these is provided by Dayan et al.7... 

The leucokinins (LK s) are a new class of insect myotropic neuropeptides isolated from head extracts of the cockroach L. maderae. These octapeptides all contain a similar core sequence of 5 amino acids that extend from position 4 through 8. This sequence Phe-X-Ser-Trp-Gly-NH2 seems to be required for hindgut stimulation. The initial response of the hindgut to the LK s was characterized by an increase in the frequency and/or amplitude of phasic contractions (50, ). At higher peptide concentrations, a tonic component was generally present. All of the LK s showed a response at 3 x 10 M that was 5-10% above the mean level of spontaneous activity. The maximum response for each of the peptides was recorded at a concentration 2.1 X 10" M. Thus, the intrinsic activities for the LK s are nearly equal because the dose-response curves have about the same asymptotic limits. A comparison of the dose concentrations that gave a half maximal response (ED q) for the 8 peptides is shown in Table I. 

In another study investigating the dose-effect and dose-response relationship between the Cd concentration in rice and urinary concentrations/prevalence of abnormal levels of markers of renal dysfunction, significant correlations between Cd concentration in rice and concentrations as well as prevalence rates of abnormal urinary p2-microglobulin, metallothionein, glucose and amino-nitrogen levels were found. The highest maximum allowable concentration of Cd in rice calculated for these indicators was 0.34 mg/kg when the uncorrected urinary value was used and 0.29 mg/kg when the creatinine corrected value was used. Both values are lower than 0.4 mg/kg, the tentative limit prescribed by the Japanese government [103]. 

Gangl et al. [74] reported a 100-fold improvement in the detection of in vivo formed DNA adducts derived from the food-derived 2-amino-3-methyhmidaz[4,5-/ quinohne (TQ, one of the heterocyclic aromatic amines, Ch. 14.5) by the apphcation of capillary LC in combination with micro-ESI-MS. As a result, the detection limit approaches 1 adduct in 10 nucleobases using 500 pg DNA. In a subsequent study [75], this technology was applied to the quantitative analysis of the IQ-dG adduct in rat liver samples in a dose-response study. The major adduct (C8-lQ-dG) could be detected at 17.5 fmol in 300 pg of liver DNA (corresponding to 2 adducts in 10 nucleobases). 

J.R. SogUa, R.J. Turesky, A. Paehler, P. Vouros, Quantification of the heterocyclic aromatic amine DNA adduct N-(deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-fjquinoline in livers of rats using capillary LC-ESI-MS A dose-response study. Anal. Chem., 73 (2001) 2819. 

Another assay, the Bradford assay, also known as the Coomassie dye binding method, was first described in 1976 [19]. In an acidic environment, proteins will bind to Coomassie dye and cause a shift from the reddish brown color (465 nm) to the blue dye protein complex read at 595 nm. The development of the color is attributed to the presence of the basic amino acids arginine, lysine, and histidine. Van der Waals forces and hydrophobic interactions account for the dye binding and the number of Coomassie blue dye molecules bound is roughly proportional to the number of positive charges on the molecule. A protein molecular weight of about 3 kDA is required for successful color development. The Bradford assay dose response is nonlinear and this method demonstrates the greatest difference in reactivity with BSA compared to BGG. 

For a hydroalcoholic extract of Hypericum perforatum, produced by successive extraction of dried aerial parts with petroleum ether, 1,2-dichlorethane and ethanol (50 % v/v), a sedative effect in mice has been reported [123]. The authors observed a bell-shaped dose-response effect on spontaneous motility with maximal activity at an oral dose of 26.5 mg/kg p.o, while pentobarbital-induced sleeping time was most significantly prolonged at the lowest dose applied (13.25 mg/kg p.o.). No effect on neuromuscular transmission was observed in three different test models (chimney test, traction test and rota-rod test). After separation of the crude extract in fractions containing mainly flavones, naphthodianthrones or amino acids, it was not possible to clearly attribute the effect of the native extract to a particular group of constituents. Thus, the authors conclude that activity of the hydroalcoholic extract may results form the cumulative effects of different compound, but they do not offer any explanation for the lower activity of the extract at higher doses. 

Peptidoglycans have been postulated as a possible causative agent for pulmonary inflammation associated with inhalation of Gm+ bacteria. Peptidoglycans are components of the cell wall envelope of bacteria and are especially prevalent in the backbone of Gm+ bacteria. They may act as endotoxin-like molecules when inhaled. Muramic acid is an amino sugar component of peptidoglycans that does not appear elsewhere in nature and is a suitable marker for analytical assays (Black et al., 1994 Fox et al., 1993 Fox et al., 1995 Sonesson et al., 1988). Although peptidoglycans have been found in hospital and home air conditioner filters (Fox and Rosario, 1994), to date there have been no systematic dose-response studies to identify their potency. 

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