Effect of Pyrithiamine Treatment and Subsequent Thiamine Rehabilitation on Regional Cerebral Amino Acids and Thiamine-Dependent Enzymes

Pyrithiamine-induced thiamine-deficiency encephalopathy in the rat shows many neuropathological and biochemical similarities to Wernicke's encephalopathy in humans. Treatment of rats with pyrithiamine resulted in moderate reductions of glutamate in thalamus and pons and in generalized severe reductions of aspartate in pons (by 89%, p less than 0.01), thalamus (by 83%, p less than 0.01), cerebellum (by 53%, p less than 0.01), and cerebral cortex (by 33%, p less than 0.05). Alanine concentrations were concomitantly increased. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase (alpha KGDH) were decreased in parallel with the aspartate decreases; pyruvate dehydrogenase complex activities were unchanged in all brain regions. Following thiamine administration to symptomatic pyrithiamine-treated rats, neurological symptoms were reversed and concentrations of glutamate, aspartate, and alanine, as well as alpha KGDH activities, were restored to normal in cerebral cortex and pons. Aspartate levels and alpha KGDH activities remained below normal values, however, in thalamus. Thus, pyrithiamine treatment leads to reductions of cerebral alpha KGDH and (1) decreased glucose (pyruvate) oxidation resulting in accumulation of alanine and (2) decreased brain content of glutamate and aspartate. Such changes may be of key significance in the pathophysiology of the reversible and irreversible signs of Wernicke's encephalopathy in humans.     

GROWTH OF LITTLE BLUESTEM (SCHIZACHYRIUM SCOPARIUM) (POACEAE) IN FUMIGATED AND NONFUMIGATED SOILS UNDER VARIOUS INORGANIC NUTRIENT CONDITIONS

Little bluestem plants (Schizachyrium scoparium (Michx.) Nash) were grown in fumigated and nonfumigated soil under manipulated levels of three inorganic nutrients: nitrogen, phosphorus, or bases (Ca + Mg). Plants grown in nonfumigated soil had significantly (P < 0.05) higher tissue levels of inorganic nutrients (Cu, Zn, Al, S, Mg, Mn, Ca, and P), smaller shoots, less total biomass, fewer flowering plants but more VAM fungal colonization than plants grown in fumigated soil that were essentially nonmycorrhizal (colonization vs. 1.2 ± 4.9%, for plants grown in nonfumigated and fumigated soil, respectively). Levels of phosphorus (14–33 μg/g) available (Bray No. 1) in the soil prior to manipulation, which are adequate for little bluestem, likely resulted in the development of an ineffectual mycorrhizal association, which in turn, caused the depressed growth of plants in nonfumigated soil. Among plants grown in nonfumigated soil, there was significant variation in VAM fungal colonization and sporulation owing to nutrient treatment. Nitrogen treatment and deionized water control had significantly lower levels of colonization than phosphorus and base treatments. However, plants in the nitrogen and base treatments had significantly more spores/100 cc of rhizosphere soil than plants grown in the deionized water control.     

Different Hoechst 33342 and DAPI fluorescence of the human Y chromosome in bivariate flow karyotypes

Summary The staining properties of AT-specific dyes Hoechst 33342 and DAPI as revealed by Hoechst 33342/mithramycin and mithramycin/DAPI bivariate human flow karyotype patterns are different for chromosomes rich in heterochromatin. The peak corresponding to chromosome Y of a given cell line is higher on the A/T axis with mithramycin/DAPI staining than with mithramycin/Hoechst. The chromosome 1 was found slightly more fluorescent in mithramycin/DAPI than in mithramycin/Hoechst as judged by the slight displacement of its area on the Hoechst-DAPI axis. The other peaks did not show major differences. On the same flow karyotypes, chromosomal rearrangements were detected.     

Inhibition by excitatory sulphur amino acids of the high-affinityl-glutamate transporter in synaptosomes and in primary cultures of cortical astrocytes and cerebellar neurons

A detailed kinetic study of the inhibitory effects ofl- andd-enantiomers of cysteate, cysteine sulphinate, homocysteine sulphinate, homocysteate, and S-sulpho-cysteine on the neuronal, astroglial and synaptosomal high-affinity glutamate transport system was undertaken.d-[³H] Aspartate was used as the transport substrate. Kinetic characterisation of uptake in the absence of sulphur compounds confirmed the high-affinity nature of the transport systems, the Michaelis constant (K _m) ford-aspartate uptake being 6 M, 21 M and 84 M, respectively, in rat brain cortical synaptosomes and primary cultures of mouse cerebellar granule cells and cortical astrocytes. In those cases where significant effects could be demonstrated, the nature of the inhibition was competitive irrespective of the neuronal versus glial systems. The rank order of inhibition was essentially similar in synaptosomes, neurons and astrocytes. Potent inhibition (K _iK _m) of transport in each system was exhibited byl-cysteate, andl- andd-cysteine sulphinate whereas substantially weaker inhibitory effects (K _i>10–1000 times the appropriateK _m value) were exhibited by the remaining sulphur amino acids. In general, inhibition: (i) was markedly stereospecific in favor of thel-enantiomers (except for cysteine sulphinate) and (ii) was found to decrease with increasing chain length. Computer-assisted molecular modelling studies, in which volume contour maps of the sulphur compounds were superimposed on those ofd-aspartate andl-glutamate, demonstrated an order of inhibitory potency which was, qualitatively, in agreement with that obtained quantitatively by in vitro kinetic studies.Special issue dedicated to Dr. Elling Kvamme     

Characterisation of chloride transport at the tonoplast of higher plants using a chloride-sensitive fluorescent probe

The characteristics of Cl^– transport in isolated tonoplast vesicles from red-beet (Beta vulgaris L.) storage tissue have been investigated using the Cl^–-sensitive fluorescent probe, 6-methoxy-1-(3-sulfonatopropyl)-quinolinium (SPQ). The imposition of (inside) positive diffusion potentials, generated with K⁺ and valinomycin, increased the initial rate of Cl^– transport, demonstrating that Cl^– could be electrically driven into the vesicles. Chloride influx was unaffected by SO ₄ ^2- , but was competitively blocked by NO ₃ ^– , indicating that both Cl^– and NO ₃ ^– may be transported by the same porter. In some preparations, increases in free-Ca²⁺ concentration from 10^–8 to 10^–5 mol·dm^–3 caused a significant decrease in Cl^– influx, which may indicate that cytosolic Ca²⁺ concentration has a role in controlling Cl^– fluxes at the tonoplast. However, this effect was only seen in about 50% of membrane preparations and some doubt remains over its physiological significance. A range of compounds known to block anion transport in other systems was tested, and some partially blocked Cl^– transport. However, many of these inhibitors interfered with SPQ fluorescence and so only irreversible effects could be tested. The results are discussed in the context of recent advances made using the patch-clamp technique on isolated vacuoles.Abbreviations and Symbols BTP 1,3-bis[tris(hydroxymethyl)-methylamino]propane - DTT dithiothreitol - EDTA ethylenediaminetetraacetic acid - membrane potential - pH pH gradient - SPQ 6-methoxy-1-(3-sulfonatopropyl)quinolinium - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl] glycine     

The use of amphipathic maleimides to study membrane-associated proteins

A series of amphiphilic polymethylenecarboxymaleimides has been synthesized for use as sulfhydryl reagents applicable to membrane proteins. Physical properties of the compounds which are relevant to their proposed mode of action have been determined. By comparing rates of reaction in aqueous and aprotic solvents, the compounds have been shown to react exclusively with the thiolate ion. The effects of the reagents on three membrane-associated proteins are reported, and in two cases a comparative study has been made of the effects on the proteins in the absence of membranes. A mechanism is proposed whereby the reagents are anchored at the lipid/water interface by the negatively charged carboxyl group, thus siting the reactive maleimide in a plane whose depth is defined by the length of the reagent. Supporting evidence for this model is provided by the inability of the reagents to traverse membranes, and variation of their inhibitory potency with chain length when the proteins are embedded in the membrane, but not when extracted into solution. As examples of general use of the reagents to probe sulfhydryl groups in membrane proteins, the reagents have been used to (a) determine the depths in the membrane at which two populations of sulfhydryl groups occur in the mitochondrial phosphate transporter; (b) locate a single sulfhydryl associated with the active site ofD--hydroxybutyrate dehydrogenase in the inner mitochondrial membrane; (c) examine sulfhydryl groups in theD-3-glyceraldehyde phosphate dehydrogenase associated with the human red blood cell membrane.     

On the nature of the photosynthetic energy storage monitored by photoacoustic spectroscopy

The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i₅₀) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.Abbreviations PS photosystem - Tes N-Tris [hydroxymethl] methyl-2-aminoethanesulfonic acid - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - FeCN potassium ferricyanide - DCBQ 2,5-dichlorobenzoquinone - TMPD N,N,N-tetramethyl-p-phenilenediamine     

Belizia brevicauda,a new genus and species of caligid copepod from the western Caribbean Sea

A new genus and species of parasitic copepod collected from the fishes Calamus pennatula and Clepticus parrae from off Belize, Central America is described. The new genus is characterized by a very reduced sternal furca, a pair of sclerotized knobs between the interpodal plates of the first and second legs, and endopod of third leg with 4 setae.