Ammonia rhythm in Microcystis firma studied by in vivo 15N and 31P NMR spectroscopy

Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo ³¹P NMR. Furthermore, the energy status of the cells remains regulated. In vivo ¹⁵N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show -aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.Abbreviations GABA -aminobutyric acid - GOGAT glutamate synthase - GS glutamine synthetase - MDP methylene diphosphonate - MOPSO 3-(N-morpholino)-2-hydroxy-propanesulfonic acid - NDPS nucieoside diphosphosugars - NOE nuclear Overhauser effect - NMR nuclear magnetic resonance For convenience, the term ammonia is used throughout to denote ammonia or ammonium ion when there is no good evidence as to which chemical species is involved     

Nectar sugar and amino acid preferences of Battus philenor (Lepidoptera, Papilionidae)

Abstract.

• 1 Butterflies of Battus philenor were tested for their preferences for nectar sugars and amino acids in an outdoor cage experiment.
• 2 The butterflies clearly preferred both sucrose and fructose over glucose. They also preferred sucrose over fructose.
• 3 No other preferences were found to be statistically significant, although male butterflies tended to prefer a plain sugar solution over a sugar solution containing a mixture of amino acids: females consumed both of these solutions in almost equal proportions.
• 4 The results are discussed with respect to nectar composition of butterfly pollinated flowers, flower preferences, physiological and reproductive aspects of butterflies.

     

Receptor sites for amino acids in the facial taste system of the channel catfish

1. Receptor sites for different amino acids in the facial taste system of the channel catfish, Ictalurus punctatus, were determined from in vivo electrophysiological cross-adaptation experiments. 2. Relatively independent receptor sites were indicated for L-proline, D-proline, D-arginine, L-histidine and L-lysine, as well as those previously reported for L-alanine, L-arginine and D-alanine. 3. The functional isolation of two nerve twigs that were more responsive to D-alanine than to L-alanine or to other test stimuli provided further evidence for the existence of D-alanine sites that are independent from those to L-alanine. 4. Under all cross-adaptation regimes, the taste responses to the majority of test stimuli were reduced. Various possible mechanisms accounting for this generalized reduction in action potential activity during adaptation are discussed.     

Neuropharmacological analysis of synaptic transmission in the Lorenzinian ampulla of the skate Raja clavata

Summary Dissected ampullae of Lorenzini of the skate (Raja clavata) were studied with the aim of determining the synaptic transmitter between electroreceptor cell and afferent fibre. Resting activity and stimulus-evoked activity in response to electrical pulses were recorded in single afferent units at constant perfusion with normal and test solutions containing different putative neurotransmitters. Presynaptic transmitter release was blocked by Mg²⁺ (up to 50 mM) to investigate the effects of the test substances upon the postsynaptic membrane. l-Glutamate (l-GLU) and l-aspartate (l-ASP), both at concentrations between 10^-7 and 10^-3 M, enlarged strongly resting and stimulus-evoked discharge frequency in the afferent fibre. If transmission was blocked by high Mg²⁺, resting discharge frequency could be restored by l-GLU or l-ASP. The glutamate agonists quisqualate (10^-8–10⁵ M) and N-methyl-D-aspartate (10^-5–10^-3 M) enlarged spontaneous activity in the afferent fiber. The same was found for kainic acid (10^-9–10^-5 M). Taurine at concentrations between 10^-5 and 10^-3 M caused a concentration-dependent decrease in afferent activity. The same was found for gammaaminobutyric acid (GABA; 10^-5–10^-4 M), and for the catecholamines adrenaline and noradrenaline, both in concentrations between 10^-5 and 10^-3 M. Serotonine (10^-5–10^-3 M) and dopamine (10^-5-10^-3 M) had no effect on resting or evoked activity in the Lorenzinian ampulla afferents. Acetylcholine (ACh; 10^-4 M) enlarged discharge frequency in those units with initial rates lower than 22–25 Hz, but diminished discharge frequency in fibres with initial activity higher than 25 Hz. When synaptic transmission was blocked by high Mg²⁺ solution, perfusion with additional ACh did not restore resting activity in the afferent fibre. The results suggest that the most probable transmitter in the afferent synapse of the ampullae of Lorenzini is l-GLU or l-ASP, or a substance of similar nature.Abbreviations ACh acetylcholine - GABA gamma aminobutyric acid - KA kainic acid - l-ASP l-aspartate - l-GLU l-glutamate - NMDA N-methyl-D-aspartate - Q quisqualate - n.s. normal solution     

Segmental release of amino acid neurotransmitters from transcranial stimulation

The present study used microdialysis techniques in an intact rabbit model to measure the release of amino acids within the lumbar spinal cord in response to transcranial electrical stimulation. Dialysis samples from the extracellular space were obtained over a stimulation period of 90 minutes and were examined using high pressure liquid chromatography. Neuronal excitation was verified by recerding corticomotor evoked potentials (CMEPs) from the spinal cord. A significant increase in the release of glycine and taurine compared to sham animals was measured after 90 minutes of transcranial stimulation. Glutamate and aspartate release was not significantly elevated. GABA concentrations were consistently low. CMEP components repeatedly showed adequate activation of descending fiber pathways and segmental interneuron pools during dialysis sampling. Since glycine, and to a lesser extent taurine, have been shown to inhibit motor neuron activity and are closely associated with segmental interneuron pools, suprasegmental modulation of motor activity may be, in part, through these inhibitory amino acid neurotransmitters in the rabbit lumbar spinal cord.     

Changes in free amino acid concentrations in serum,brain, and CSF throughout embryogenesis

Using the developing chick embryo as a model and a very sensitive micromethod for amino acid analysis, a complete analysis is presented of the developmental changes in free amino acid concentration in the blood, in the CSF, and in two different brain regions (optic lobe and frontal lobe) of the chick embryo (from day 4 of incubation, until day 5 post hatching). The developmental profile of Lys is the only one that is almost identical in all three compartments. The developmental profiles of the serum and of the brain are very similar for Arg and Phe, less so for Leu and Gly, and towards the end of the embryonic period, similar also for Val, Ile, Trp, and Met. The amino acid concentrations in the CSF are either much lower than in serum and brain already at the earliest stages, or they progressively decline to levels lower than those in brain and serum, most rapidly between day 6 and 8 of embryonic life. The concentrations of neuroactive amino acids (Gln, Glu, Asp, GABA, Tau, and Gly) in both brain regions begin to increase very early, and continue to rise, except Tau, which goes through a maximum at day 8. Comparative analysis of the developmental profiles of each amino acid in serum, brain, and CSF reveals that the blood supply and the cellular uptake, retention, and metabolism by neural cells are the major determinants of the free amino acid pool of the developing brain.     

Resistance in the wild crop relatives Avena macrostachya and Hordeum bogdani to the aphid Rhopalosiphum padi

In previous screening tests the two wild crop relatives Avena macrostachya (Bal., ex Coss. et Dur.) and Hordeum bogdani (Wil.) demonstrated a high degree of resistance to the aphid Rhopalosiphum padi (L.). In a choice situation using wild and cultivated oats and barley, alate aphids settled in lower numbers on the wild species. The results were, however, variable in the Avena combination. Nymph production was significantly higher, development time shorter and adult weight higher on the cultivated varieties. From the third instar and onwards the excretion of honeydew was significantly lower on the resistant plants. In general the honeydew contained less than 1% free amino acids although excreta from H. vulgare contained 3.5%. The percentage of free amino acids found in the honeydew was similar for all plant species (5.2–7.6%) except for H. vulgare, on which the aphids excreted 22% of the amounts ingested. Amino acids excreted in high proportions on all plants included asparagine, -aminobutyric acid, glutamic acid, and glycine. Tissue sectioning did not reveal any obvious mechanical barriers to stylet penetration. The potential use of these wild species as sources for aphid resistance breeding in oats and barley is considered.

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Résumè Lors d'examens systématiques antérieurs, Avena macrostachya (Bal. ex Coss. & Dur.) et Hordeum bogdani (Wil.) ont présenté une résistance élevée au puceron Rhopalosiphum padi (L.). Lorsqu'ils avaient un choix comprenant de l'avoine et de l'orge cultivés, les pucerons ailés ont atterri en nombres moins importants sur les espèces sauvages. Les résultats étaient cependant variables dans le complexe avoine. La production de nymphes et le poids des adultes étaient plus élevés sur espèces cultivées, ainsi que la durée du développement était plus longue sur les espèces sauvages. A partir du troisième stade, l'excrétion de miellat a été significativement plus faible sur les espèces résistantes. En général, le miellat y contenait moins de 1% d'acides aminés bien que sur H. vulgare il en contînt 3,5%. Les pourcentages d'acides aminés libres du miellat étaient semblables sur toutes les plantes (5,2–7,6%), à l'exception de H. vulgare sur lequel les pucerons excrétaient 22% des taux ingérés. Les acides aminés excrétés en fortes quantités sur les différentes plantes, comprenaient l'asparagine, l'acide -aminobutyrique, l'acide glutamique et la glycine. Des coupes de tissus n'ont révélé aucun obstacle mécanique clair à la pénétration des stylets. Les possibilités d'utiliser ces espèces sauvages comme source de résistance aux pucerons dans la sélection de l'avoine et de l'orge ont été examinées.

     

Resistance of different lucerne cultivars to the pea aphid Acyrthosiphon pisum: influence of phloem composition on aphid fecundity

Sugars and amino acids were analysed in the phloem sap (sampling by the exudation method) of four clones of lucerne (Medicago sativa L.) characterized by their resistance to the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Differences in the qualitative amino acid balance are shown and a negative correlation between the reproductive rate of the aphid and the sugars/amino acids ratio is underlined. To demonstrate any causal relationship between these two variables, the reproduction of A. pisum on artificial diets copying the sap of the two extreme clones (resistant and susceptible) was measured. The results show that the resistance is not a simple nutritional effect; however, the amino acid balance contributes to the resistance exhibited by some cultivars.

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Résumé L'analyse (sucres et acides aminés) de la sève de 4 cultivars de luzerne (Medicago sativa) caractérisés pour leur résistance au puceron du pois (Acyrthosiphon pisum (Harris)) (Homoptera: Aphididae), est réalisée sur des exsudats de phloème. La teneur en sucres (exprimée en équivalent saccharose) montre d'importantes différences: rapport de 1 à 3 respectivement entre les clones sensible et résistant. La teneur globale en acides aminés exsudés varie en sens inverse, entraînant une corrélation négative pour les 4 clones étudiés entre le rapport sucre/acides aminés (0,6 à 3,6) et la résistance mesurée par le taux net de reproduction à 14 jours (78,5 à 11,2 larves/femelle). L'analyse des acidses aminés révèle de plus des différences qualitatives entre cultivars, notamment pour certains acides aminés essentiels méthionine, histidine, lysine, aromatiques.Le rôle de l'équilibre en acides aminés et en sacharose dans la résistance de certains cultivars au puceron du pois est apprécié par des mesures de la reproduction de A. pisum sur des milieux artificiels reproduisant le rapport sucre/acides aminés et/ou le spectre des acides aminés des 2 clones extrêmes (sensible et résistant). La résistance n'apparaît pas être le résultat d'une simple différence de la qualité nutritionnelle de la sève; la balance en acides aminés doit cependant participer pour une part à la résistance au puceron.

     

Human heart cytochrome c oxidase subunit VIII. Purification and determination of the complete amino acid sequence

Subunit VIII was purified from a preparation of the human heart cytochrome c oxidase and its complete amino acid sequence was determined. The sequence proved to be much more related to that of the bovine liver oxidase subunit VIII than to that found in bovine heart. Our finding of a ‘liver-type’ subunit VIII in the human heart enzyme suggests that either there are no isoforms of human subunit VIII or the human oxidase does not show the type of tissue specificity that has been reported for the oxidase in other mammals.     

Determination of intermediates, products and cleavage site in the reaction between plasminogen activator inhibitor type-2 and urokinases

Several specific inhibitors for plasminogen activators have been isolated from various organs and cell lines, those from human placenta and the human monocyte-like cell line U-937 being virtually identical. The reaction between this type of inhibitor, designated as type-2, and high-M_r and low-M_r urokinase-type plasminogen activators was followed by reversed-phase high-performance liquid chromatography and gel electrophoresis. The components, their stable complexes and their dissociation and cleavage products could be clearly identified in both systems. The amino acid sequence of the inhibitor at the cleavage site was determined to be -Met-Thr-Gly-Arg↓Thr-Gly-His-Gly-. A 35-residue carboxy-terminal fragment was found to be released.