Effects of FMRFamide-related peptides and morphine on the isolated foregut of the locust Schistocerca gregaria.

1. Morphine and YAGFMamide were the most effective potentiators of 5-hydroxytryptamine (5-HT)-induced relaxation of the isolated foregut. 2. Morphine had no effect on proctolin-induced tissue contraction which was inhibited by YGGFMamide and YFMRFamide. 3. The differing potency of FaRPs and morphine to potentiate 5-HT effects and reduce proctolin responses suggests that there are two separate FaRP receptor sub types. 4. This proposal is supported by the observation that, while naloxone (10(-5) M) is a relatively potent antagonist of FaRP induced inhibition of proctolin contraction, it has less effect on FaRP-induced potentiation of 5-HT-induced relaxation.

Tyramine antagonizes proctolin-induced contraction of the isolated foregut of the locust Schistocerca gregaria by an interaction with octopamine2 receptors.

1. Octopamine (OA) (10(-7)-10(-5) M) relaxed isolated foreguts. Tyramine mimicked the effects of OA but was 64x less potent. 2. Proctolin (10(-8) M to 10(-6) M) induced contraction of isolated foreguts was antagonised non competitively by tyramine. 3. Mianserin (10(-6) M) was a non competitive antagonist of relaxation caused by tyramine but was without effect on proctolin induced contraction. 4. Caffeine (1 microM and 2 microM) caused non competitive inhibition of proctolin-induced tissue contraction. 5. It is concluded that tyramine antagonises proctolin-induced contraction of the foregut by activating an adenylate cyclase-linked OA2 receptor.

Abscisic acid binding to subcellular fractions from leaves of Vicia faba.

A centrifugation binding assay has been used to demonstrate the binding of [(3)H] (±) abscisic acid to membrane-rich fractions prepared from leaves of Vicia faba L. Kinetic analysis of this binding shows evidence of saturation of binding sites with increasing concentration of ligand. Scatchard analysis of these data yields a biphasic plot possibly indicating the presence of two types of binding sites. The dissocation constant for the high affinity site has been calculated to be 3.5×10(-8) mol 1(-1).

The identification of the site of action of NN'-dicyclohexylcarbodi-imide as a proteolipid in mitochondrial membranes.

Mitochondrial membranes were incubated with NN'-dicyclohexyl[(14)C]carbodi-imide, which irreversibly inhibited the partial reactions of oxidative phosphorylation by 95-100%. Solutions of the membranes were analysed on polyacrylamide gels. Of the radioactivity recovered from the gels 90% was shown to be associated with a single protein of molecular weight about 10000. The radioactive protein and associated phospholipid was solubilized from the membrane by extraction with chloroform-methanol mixtures and was concentrated 50-fold by solvent fractionation and adsorption chromatography on Sephadex LH-20. Several protein-radioactivity peaks were obtained by Sephadex LH-20 chromatography. However, 90-100% of the radioactivity in each peak was shown to be associated with a single protein similar to the major radioactive protein observed in electrophoretograms of the membrane solutions. It is concluded that dicyclohexylcarbodi-imide inhibits mitochondrial oxidative phosphorylation by reacting covalently with a group on this chloroform-methanol-soluble protein. The possible role of this protein in oxidative phosphorylation is discussed.