Inhibition of the NADP-linked glutamate dehydrogenase from Trypanosoma cruzi by silver nitrate.

The purified NADP-linked glutamate dehydrogenase from Trypanosoma cruzi was strongly inhibited by silver nitrate. The inhibition was reversed by reduced glutathione, and was modified by the presence of the substrates during preincubation of the enzyme with the inhibitor.     

Inactivation of human glutamate dehydrogenase by aluminum

Aluminum inactivated glutamate dehydrogenase (GDH) by a pseudo-first-order reaction at micromolar concentrations. A double-reciprocal plot gave a straight line with a k_inact of 2.7 min^-1 and indicated the presence of a binding step prior to inactivation. The inactivation was strictly pH dependent and a marked increase in sensitivity to aluminum was observed as the pH decreased. At a pH higher than 8.5, no inactivation was observed. The completely inactivated GDH contained 2 mol of aluminum per mole of enzyme subunit monomer. When preincubated with enzyme, several chelators such as citrate, NaF, N-(2-hydroxyethyl) ethylenediaminetriacetic acid or ethylenediaminetriacetic acid efficiently protected the enzyme against the aluminum inactivation. In a related experiment, only citrate and NaF released the aluminum from the completely inactivated aluminum-enzyme complex and fully recovered the enzyme activity. Ferritin, NADP⁺, or nerve growth factor did not show any effects on the recovery of the aluminum-inactivated GDH activity. The dissociation constant for the aluminum-enzyme complex was calculated to be 5.3 M. Although aluminum has been known to form a complex with nucleotides, no such effects were observed in the inactivation of GDH by aluminum as determined using GDHs mutated at the ADP-binding site, NAD⁺-binding site or GTP-binding site. Circular dichroism studies showed that the binding of aluminum to the enzyme induced a decrease in helices and sheets and an increase in random coil. Therefore, inactivation of GDH by aluminum is suggested to be due to the conformational change induced by aluminum binding. These results suggest a possibility that aluminum-induced alterations in enzymes of the glutamate system may be one of the causes of aluminum-induced neurotoxicity.Received 25 July 2003; received after revision 27 August 2003; accepted 15 September 2003     

Interaction of benznidazole reactive metabolites with nuclear and kinetoplastic DNA,proteins and lipids fromTrypanosoma cruzi

Summary Epimastigotes ofTrypanosoma cruzi (Tulahuen strain Tul 0 stock) biotransform benznidazole (N-benzyl-2-nitro-1-imidazone acetamide) to reactive metabolites that bind covalently to DNA, proteins and lipids of the parasite. These effects might be related to the trypanocidal action of benznidazole, a chemotherapeutic agent against Chagas' disease.     

Lactate dehydrogenase and glutamate dehydrogenase activities in the circumventricular organs of rat brain following neonatal monosodium glutamate

Glutamate (glu) an excitatory neurotransmitter amino acid, is present in high concentrations in the mammalian central nervous system and is the most abundant amino acid in our daily diet. In the present study the activities of lactate dehydrogenase (LDH) and glutamate dehydrogenase (GDH) were evaluated in the circumventricular organs (CVO) of the brain in 25-day-old rats following MSG administration at a dose of 4 mg/g b.wt during the first ten days of life. The results show the LDH activity increased to 265% of that in the control (p<0.001), whereas GDH activity was significantly decreased (p<0.05), The great elevation in LDH, a cytoplasmic marker enzyme, is apparently due to cytoskeletal changes brought about as a consequence of glu toxicity, whereas lowered GDH activity indicates altered glu homostasis in the blood-brain-barrier deficient areas following neonatal exposure to glu.     

Hormonal induction of glutamate dehydrogenase in rat liver

Summary Glutamate dehydrogenase rapidly increases in microsomes and appears in the cytoplasm after administration of cortisone, cAMP, hydrocortisone-acetate. Prolonged administration of ACTH maintains high level of enzyme in the mitochondria and microsomes. Hydrocortisone-acetate, insulin and corticosterone decrease drastically enzyme in mitochondria.Supported by N.I.H. grant Nr. PR 0806-02.     

Hormonal induction of glutamate dehydrogenase in rat liver.

Glutamate dehydrogenase rapidly increases in microsomes and appears in the cytoplasm after administration of cortisone, cAMP, hydrocortisone-acetate. Prolonged administration of ACTH maintains high level of enzyme in the mitochondria and microsomes. Hydrocortisone-acetate, insulin and cortisone decrease drastically enzyme in mitochondria.     

Inhibition of liver lactate dehydrogenase by serotonin: Possible relationship to endotoxin effects

Zusammenfassung Serotonin hemmt die Lactatdehydrogenase im Lebercytosol von Kaninchen in vitro. Für eine 10%ige Aktivitätshemmung gegenüber den Kontrollwerten genügte eine durchschnittliche Konzentration von 9,15 /ml, die nur etwa zweimal höher liegt als der normale Blutspiegel. Dieser Effekt ist möglicherweise an der im Verhältnis zum Sauerstoffdefizit auffallend geringen Lactatbildung im Endotoxinschock beteiligt.

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Work supported by Research Grant No. 3.10.68 from the Swiss National Foundation for Scientific Research.     

Inhibition of human testicular glucose-6-phosphate dehydrogenase by unsaturated C19-steroids

Zusammenfassung Die Bebrütung einer gereinigten G-6-PDH aus menschlichem Testisgewebe mit 3-substituierten ⁴- oder ⁵-C₁₉-Steroiden zeigte, dass 3-Hydroxy-⁴-oder ⁵-androsten-17-on auch wirksame Inhibitoren der testikulären G-6-PDH darstellen. Zur gleichen Zeit konnten die früher gefundenen Zusammenhänge zwischen chemischer Struktur eines Steroids und seiner biologischen Aktivität im G-6-PDH-Hemmtest uneingeschränkt bestätigt werden.     

A simple silver nitrate impregnation of nerve fibres with preservation of acetylcholinesterase activity at the motor end-plate

Summary A rapid silver nitrate impregnation of nerve fibres has been devised to maintain a histochemically detectable acetylcholinesterase activity at the motor end-plates.We thank Mrs Paulette Cloup and Mr D. Levieux for their valuable technical assistance.     

A simple silver nitrate impregnation of nerve fibres with preservation of acetylcholinesterase activity at the motor end-plate

A rapid silver nitrate impregnation of nerve fibres has been devised to maintain a histochemically detectable acetylcholinesterase activity at the motor end-plates.     

On the mechanism of killing ofTrypanosoma cruzi by human polymorphonuclear leukocytes

Summary The temperature-dependence of some processes involved in the killing of sensitizedT. cruzi epimastigotes by human polymorphonuclear leukocytes (PMN) was determined. The rate of the reactions was related to the temperature of incubation according to the Arrhenius equation and the apparent energies of activation (Ea) were calculated. The Ea values separated these complex reactions into two groups: one with Ea of about 10 kcal/mol for the phagocytosis of the parasites and the release of lysosomal enzymes by PMN, and the other with Ea of about 22 kcal/mol for the cytotoxicity against sensitizedT. cruzi, the rate of oxygen consumption by PMN, and the lysis of the parasites with added hydrogen peroxide.This work was supported by research grants from CONICET and SUBCYT, Argentina, and UNDP/Word Bank/WHO Special Programme for Research and Training in Tropical Diseases. The author wish to thank Dr I. Reisin, Dr. A. Boveris and Dr M.M.E. de Bracco for their helpful discussion.     

The toxic action of halogenated alkylating substances on insects. Inhibition of triosephosphate dehydrogenase

Zusammenfassung Nachdem die Verfasser auf ihre früheren Aufsätze über die auf Insekten wirkenden alkylisierten halogenierten Stoffe hingewiesen haben, fassen sie die Ergebnisse zusammen, die sie bei der Wirkung der genannten Stoffe auf die in den Muskelgeweben vonP. americana undM. domestica befindlichen Triosephosphatdehydrogenasen (TPD) erzielt haben.Die Dosierung der TPD ist kolorimetrisch bestimmt worden, indem 2,6-Dichlorphenol-Indophenol als Wasserstoffakzeptor gebraucht wurde.Es hat sich gezeigt, dass TPD sowohlin vitro wiein vivo inhibiert wird. In Hausfliegen hat die Mortalität der Fliegen und die TPD-Inhibition bezüglich der verschiedenen Stärken der Dichloressigsäure einen parallelen Verlauf, und die Inhibitionswerte sind niedriger als die der Mortalität.Hausfliegenstämme, die während 20 Generationen hindurch im Chloressigsäurekontakt selektioniert wurden, weisen weder eine auffällige Resistenzzunahme gegen diesen Stoff noch eine Steigerung von TPD in den Extrakten dieser Fliegen auf.     

Inhibition of the masseteric reflex by vagal afferents

Zusammenfassung Es wurde an der kurarisierten Katze bei «encéphyle isolé» der Einfluss sensibler Vagusfasern auf den monosynaptischen Reflex des Musculus massetericus untersucht (für alle Fasergruppen des Vagus überschwellige Reize). Vollständige Hemmung des Masseter-Reflexes wurde erzielt bei Reizung des proximalen Endes des Halsvagus mit Einzelstromstössen oder kurzen Serien.

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This research was supported by a grant from the U.S.P.H.S. (No. MH-10083). This work has received bibliographic aid from the UCLA Brain Information Service which is a part of the National Information Network of the NINDB and supported under Contract No. PH-43-66-59.     

Inhibition of the apomorphine gnawing compulsion by amantadine

Zusammenfassung Amantadin bewirkte bei Ratten eine dosisabhängige Hemmung der sogenannten Apomorphin-«Gnawing Compulsion» und verhielt sich somit ähnlich wie ein Dopaminrezeptorblocker.     

Ultrastructural identification of the nucleolus organizer by the silver staining technic]

The nucleolus organizer regions can be selectively stained in metaphase chromosome preparations by the Goodpasture and Bloom's technique which was adapted to electron microscopy analysis of cells during interphase. Using this technique, a selective accumulation of silver grains was observed over nucleolus light areas. This selective accumulation allows the identification of the interphase fibrillar centers as the nucleolus organizer regions. Ultrastructural relationships between fibrillar centers and dense fibrillar component are discussed.