Orders Of Magnitude Higher Affinity Research Articles

ChemInform Abstract: Thienylpyrazoloquinolines: Potent Agonists and Inverse Agonists to Benzodiazepine Receptors.

AbstractCoupling of the 4‐chloroquinoline derivatives (I) with the 3‐hydrazinothiophene (II) gives the adducts (III) which are cyclized, forming the fused quinolines (IV).

Towards assignment of secondary structures by anti-peptide antibodies. Specificity of the immune response to a beta-turn.

In an attempt to assign secondary structure elements to protein primary structures with antibodies, we synthesized a model peptide (beta-peptide: TVTVTDPGQTVTY) with a putative beta-turn structure and analysed the anti-peptide antibodies for their specificity towards the turn sequence. At least 50% of the peptide fraction adopts the intended conformation of a beta-turn (DPGQ) inserted between the two segments of an antiparallel beta-sheet structure. The specific anti-beta-peptide antibodies of the hyperimmune response bind the beta-turn containing epitope of the immunogenic beta-peptide with a three orders of magnitude higher affinity than the synthetic control peptide (Gly-peptide: GGGGGDPGQGGGG). The affinity of the antibodies with specificity for the beta-turn region increases from the primary to the hyperimmune response. Therefore, probing of secondary structure elements, i.e., of individual beta-turn regions, by anti-peptide antibodies now seems feasible for proteins of known sequence and may result in sequence assignments of secondary structures.

Characterization of the spinal adrenergic receptors mediating the spinal effects produced by the microinjection of morphine into the periaqueductal gray

After the microinjection of morphine (5 μg/0.5 μl) into the periaqueductal gray resulted in an increase in the hot-plate and tail-flick response latency of the unanesthetized rat, the α-adrenergic antagonists yohimbine, rauwolscine and corynanthine were given intrathecally. This treatment resulted in a dose-dependent reversal of the inhibition of the thermally evoked tail-flick reflex. The relative potency of these stereoisomers was: yohimbine=rauwolscine>corynanthine. Given the reported affinity of these agonists for the α 2 (yohimbine/rauwolscine) and α 1 (corynanthine) receptors, these observations suggest that the spinopetal noradrenergic systems are acting on α 2-adrenergic receptors. Prazosin, an agent with several orders of magnitude higher affinity for the α 1than theα 2-receptor , was at best only equiactive with yohimbine. None of the intrathecal treatments produced a significant reversal of the effects of periaqueductal gray morphine on the hot-plate response. This suggests that the activation of spinopetal noradrenergic pathways alone cannot account for the suppression by morphine in the periaqueductal gray of this response which is organized at the supraspinal level.

Hepatic α-adrenoreceptor: Specific and irreversible labeling by [ 3H]-phenoxybenzamine

The binding of [ 3H]-phenoxybenzamine, a potent irreversible alpha-adrenergic antagonist, to alpha-adrenergic binding sites in rat liver plasma membranes was a saturable process with a number of binding sites of 1600 fmol/mg of membrane protein. No significant dissociation of this ligand occurred after dilution for 2 hours, or repeated washing of the labeled membranes. The specificity of the binding site was characterized by an order of potency of various drugs typical for an alpha-adrenergic receptor. Binding showed strict stereospecificity since R(+)phenoxybenzamine exhibited a two order of magnitude higher affinity than its S(−)isomer. A SH group was involved in the binding of both [ 3H]-phenoxybenzamine and [ 3H]-dihydroergocryptine to alpha-receptor. It appears therefore that [ 3H]-phenoxybenzamine binds irreversibly and specifically to the alpha-adrenoreceptor and that it might prove adequate in the solubilization and purification of the alpha-adrenoreceptor.