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Seven keto analogs of acetylcholine were synthesized and evaluated as inhihitors of human placental choline acetyltransferase. Their potencies for inhibition of horse serum cholinesterase and stimulation of cholinergic receptors in the longitudinal ileal muscle of the guinea pig were investigated. The most potent and selective inhibitor of choline acetyltransferase was (2-benzoylethyl)trimethylammonium chloride with an I50of 3 × 10–6M. It exhibited considerably low activities at muscarinic and nicotinic receptors and cholinesterases. Its high potency for inhibiting choline acetyltransferase was attributed to: (a) its cationic terminal, a site for an electron acceptor interaction; (b) an aryl moiety for hydrophobic and electron donor contributions; and (c) a positive charge on the carbon atom adjacent to the benzene ring due to the presence of the carbonyl group, which interacts with the nucleophilic residue on the enzyme.

Synaptosomes were prepared from rat cerebral cortex and incubated in [3H]choline for periods ranging from 1 to 90 min. The [3H]ACh synthesized during this period was found only in the cytoplasm and in a membrane-associated fraction. A negligible amount of the newly formed [3H]ACh was recovered in the vesicular fraction despite concerted efforts to protect a hypothetical population of labile vesicles. The specific activity of the membrane-associated component, accounting for 21% of the total [3H]ACh, was by far the highest. This membrane-associated fraction was not released by hypotonic shock or homogenization and apparently was not in association with the monodisperse synaptic vesicles. The [3H]ACh was released in a calcium dependent manner. This investigation has determined that the ACh synthesized by synaptosomes is localized in only two fractions, cytoplasmic and membrane-associated; that this newly synthesized ACh can be released from synaptosomes by a process consistent with physiological release; and that at least part of the ACh released was originally present in the cytoplasm.

The freshwater cyanobacterium Anabaena variabilis Kütz. (ATCC 29413) is capable of growing at concentrations of NaCl up to 250 mm under N2-fixing conditions. Nitrogenase activity was inhibited within 30 min of exposure to NaCl and a recovery of activity was observed within 24 h. An increase in the internal free pool of glutamate and a decrease in the free pool of glutamine was observed, indicating that an inhibition of the NH4+-assimilating enzyme, glutamine synthetase (GS), occurred in vivo, although only a slight inhibition of GS activity by NaCl was detected in vitro. Electron transport was found to be salt sensitive via the formation of the complex between ferredoxin and ferredoxin-NADP oxidoreductase (FNR). Nitrogenase activity was the most salt-sensitive of the enzyme processes studied.

Mothers who smoke cigarettes during pregnancy give birth to babies with lower birth weights than do nonsmoking mothers. One hypothesis to explain this finding is that nicotine depresses the activity of the placental cholinergic system, which has been linked to the placental transport of amino acids and other substances. The levels and activities of several components of the term placental cholinergic system were determined in smokers and nonsmokers to investigate whether this system is involved in the effect of smoking. There were no statistically significant differences in the levels, synthesis or release of acetylcholine in the tissues from smoking and nonsmoking mothers, nor in the activities of the choline uptake system or the enzymes choline acetyltransferase, cholinesterase or sodium/potassium adenosine triphosphatase. The results do not support the hypothesis that the lower birth weights of babies born to smoking mothers is mediated by an effect of nicotine or other tobacco components on the placental cholinergic system.

Synechococcus PCC 6301 synthesized sucrose as a compatible solute following hyperosmotic shock induced by NaCl. Initial rates of photosynthetic 14C incorporation were reduced following salt shock. Photosynthetic rates were comparable in cells enriched for glycogen (by growth in NO3--deficient medium) and cells grown in NO3--sufficient medium in the absence of osmotic shock. Incorporation of 14C was predominantly into the NaOH fraction and the residual acidic fraction in cells grown in NO3--sufficient medium, whereas incorporation was predominantly into the residual acidic fraction in cells grown in NO3--deficient medium. Following salt stress, 14C incorporation was initially into the ethanol-soluble fraction and the majority of tracer was recovered in sucrose. Carbon-14 was detected in sucrose in cells which had been enriched for [14C]glycogen prior to salt stress, inferring that glycogen can act as a carbon source for sucrose synthesis following salt stress. Changes in the specific activity of sucrose are consistent with an initial synthesis of sucrose from glycogen followed by synthesis of sucrose using newly fixed carbon, in response to salt stress.

The growth of cyanobacteria in natural waters may be dependent on an efficient ammonium transport system. Such a system may also play a role in the retention of internally generated ammonium from N2 fixation, nitrate reduction, and photorespiration. Methylammonium is commonly used as an ammonium analogue to study transport. The kinetics of methylammonium uptake by cyanobacteria are biphasic with a first rapid phase representing transport into the cells and a second slower phase dependent on metabolism by the primary ammonia assimilating enzyme glutamine synthetase. At high external pH values (pH > 9) diffusion of the uncharged species becomes increasingly dominant while at neutral pH values the uptake is thought to be an active process dependent on membrane potential.

The cyanobacteria Anabaena variabilis and Nostoc CAN showed a biphasic pattern of 14CH3NH3+uptake at external pH values of 7.0 and 9.0. The initial phase of uptake, which was independent of metabolism of 14CH3NH3+, was attributed to uptake via a CH3NH3+(NH4+) transport system at pH 7.0 and probably to passive diffusion of uncharged CH3NH2 and trapping by protonation at pH 9.0. The second slower phase of uptake was attributed to metabolism of CH3NH3+via glutamine synthetase to form ?-methylglutamine which accumulates. Anabaena cylindrica showed an initial rapid uptake at pH 7.0 and pH 9.0 but metabolism of 14CH3NH3+was undetectable at pH 7.0 and was barely detectable at pH 9.0. Pretreatment of A. variabilis with l-methionine-d,l-sulphoximine to inactivate glutamine synthetase, inhibited the second phase of 14CH3NH3+uptake at both pH 7.0 and pH 9.0 and the accumulation of ?-methylglutamine but had no effect on the first phase of uptake. Following transfer of A. variabilis to darkness the initial phase of 14CH3NH3+uptake at pH 7.0 and 9.0 was unaffected but the subsequent metabolism via glutamine synthetase was inhibited.