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1. The interaction of the vasoactive intestinal peptide family of hormones with synaptic membranes from guinea pig brain was examined using lZ5I-labeled vasoactive intestinal peptide as a tracer molecule. Binding of this peptide was rapid and temperature-dependent, as well as reversible and saturable. Scatchard plots were compatible with the existence of two classes of binding sites, the first class with an apparent & of 36 nM and a low binding capacity (4 pmol vasoactive intestinal peptide/mg membrane protein) and a second class of binding sites with a lower affinity (apparent K d of 285 nM) and a higher capacity (20 pmol vasoactive intestinal peptide/mg membrane protein).2. The specificity of binding sites for vasoactive intestinal peptide was established from the fact that binding of the '251-labeled peptide was inhibited by the unlabeled peptide and by higher concentrations of unlabeled secretin but not by the parent hormone glucagon or by the neuropeptides somatostatin, bombesin, C-terminal octapeptide of pancreozymin, Leu-enkephalin, and substance P.3. Nai, K', Ca2+, Mg2+ and EDTA reduced the amount of 1251-labeled vasoactive intestinal peptide bound at equilibrium. The monovalent and divalent cations decreased the binding rate constant, whereas EDTA increased the dissociation rate constant of binding.4. Nucleoside triphosphates and diphosphates decreased binding of the '251-labeled peptide at equilibrium and increased the rate constant of dissociation of membrane-bound vasoactive intestinal peptide. Guanyl nucleotides were the most potent and in this class of nucleotides GTP was 6-fold more potent than guanosine 5'-[P,y-imido]triphosphate.

The electroreduction of nitrate ions is investigated in acid and neutral aqueous solutions (HClO4 and NaClO4 as electrolytes) at polycrystalline copper electrodes, copper single crystals and at copper particles deposited in polyaniline (PANI) layers. In the presence of low nitrate concentrations (5 mM), the reduction of nitrate is not significantly different on various copper atomic surface structures but is greatly dependent on the local pH at the electrode. In contrast to strong acidic solutions, two separate waves are detected when nitrate ions are present in neutral solutions irrespective of the use of copper polycrystalline or single crystal electrodes. The first of the two waves leads to the formation of nitrite ions. When copper particles are dispersed in polyaniline layers it is demonstrated that the electrocatalytic activity is strongly dependent on the way of depositing copper in the polymer layer. A clear difference is observed in the current response in absence and presence of nitrate ions for copper deposited in the reduced state of the PANI layer, whereas copper deposited in the oxidized state of the PANI layer remains still electrocatalytically rather inactive. Copper crystalline species act effectively for the investigated reaction only if copper conducting paths are available through the polymer matrix up to the underlying metal surface.

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