The rates of exchange of 2-hydrogens in 3,4-dimethyloxazolium ion, 3,4-dimethylthiazolium ion, and 1,3,4-trimethylimidazolium ion have been measured at a variety of pH's and buffer concentrations. In each case the rate constant for exchange catalyzed by OD~has been evaluated. The relative second-order rate constants are respectively 105•1 2345:103•5:1. The 18C-H coupling constants for ring hydrogens have also been measured. These data for rates are compared with knowledge of the ground states. The similarity of 18C-H coupling constants in homologous imidazolium and thiazolium ions at the 2 position indicates that these C-H bonds are similar in the ground state. The exchange rate 3000 times greater in 3,4-dimethylthiazolium ion than in 1,3,4-trimethylimidazolium ion suggests the transition state for ylide formation must be considerably stabilized in the case of the sulfur heterocycle. This indicates a special role for sulfur and provides partial understanding of the importance of a thiazolium ion in the structure of thiamine.

The interaction between the alpha 2- and beta 2-adrenergic receptors of ciliary processes has been studied by examining dose-response curves for adrenergic agonist stimulation of cyclic AMP production by intact, excised rabbit ciliary processes. Stimulation of cyclic AMP production by 1-isoproterenol is maximum from 0.1 to 1.0 microM; at higher concentrations stimulation decreases and approaches basal levels. Decreased cyclic AMP production at high concentrations of isoproterenol is blocked by the specific alpha 2-adrenergic antagonist, yohimbine, but not by the alpha 1-adrenergic antagonist, prazosin. Ciliary processes from animals after bilateral cervical ganglionectomy also show reduced cyclic AMP production at high concentrations of isoproterenol and this reduction is blocked by yohimbine, but not prazosin. This experiment suggests that the inhibition at high concentrations of isoproterenol is mediated by postsynaptic alpha 2-adrenergic receptors. Cyclic AMP production is relatively insensitive to epinephrine and norepinephrine, but their responses are potentiated by yohimbine. Catecholamines and clonidine, a specific alpha 2-adrenergic agonist, exhibit dose-dependent inhibition of forskolin-stimulated cyclic AMP production by ciliary processes. I50s from the dose-response curves are consistent with the characteristic binding affinities of these adrenergic agonists for alpha 2-adrenergic receptors: clonidine = epinephrine greater than norepinephrine greater than isoproterenol. Inhibition of forskolin-stimulated cyclic AMP production by clonidine is blocked by yohimbine but not by prazosin.(ABSTRACT TRUNCATED AT 250 WORDS)

2213not valid for the transitions to the unoccupied orbitcm-I transition. This will be a very important conals. The neglect of configuration interaction may sideration for the description of other transition-metal account for the failure to predict accurately the 43,100-complexes.The pK,'s of the protonated forms of several oxazoles, thiazoles, and imidazoles have been determined and are given in parentheses following the name of the compound : 4-methyloxazole (1.07), ethyl 4-methyloxaeole-5-carboxylate (0.83), 4-methyloxazole-5-carboxylic acid (1.09, 2.88), 4-methylthiaeole (3.07), ethyl 4-methylthiazole-5-carboxylate (1.69), 4-methylthiazole-5-carboxylic acid (pKHA = 3.51), 4-methylthiazole-2-carboxylic acid (1.20, 3.18), 4-methylimidazole-5-carboxylic acid (2.53, 7.02), and l-methylimidazole-2-carboxylic acid (1.53, 7.25). Therefore, oxazoles are -lOB less basic than imidazoles, and thiazoles are w104 less basic than imidazoles. The pK's for azolium acids indicate that zwitterionic forms are favored for imidazole acids, but uncharged forms are favored for thiazole and oxazole acids.

No abstract

A solid phase enzyme-linked immunosorbent assay for quantitation of substance P is presented. The assay measures the capacity of soluble substance P to compete with the solid phase antigen for a limited quantity of specific substance P antibody. The solid-phase antigen consists of a synthetic substance P.poly-D-glutamic acid conjugate coated to polystyrene micro-ELISA plate wells. Soluble substance P and antibodies to substance P are first preincubated together and then added to the wells containing solid-phase antigen. Subsequently the wells are incubated with anti-antibodies conjugated to alkaline phosphatase. The wells are finally incubated with p-nitrophenyl phosphate an the absorbance is read in a spectrophotometer 16--24 hr after the start of the assay. The threshold for detection of substance P was 5--10 pg per well (0.25 ml). Substance P was extracted from rabbit eyes and the values obtained with the present method are compared with previously reported values based on radioimmunoassay.