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At least 163 records · Page 9Linked to original sources
PubMed1975

The effect of pyruvate on nitrogenase activity in the blue-green alga Anabaena cylindrica.

Exogenous pyruvate added to cultures of the blue-green alga, Anabaena cylindrica stimulated nitrogenase activity (measured by acetylene reduction) only in the dark under low pO2 (0.05 atmospheres). Under aerobic conditions or in the light, stimulation was absent and replaced by an inhibition of activity above 5 mM added pyruvate. The curve of nitrogenase activity versus oxygen concentration had a similar maximal value of ethylene production with, or without added pyruvate, but in the presence of pyruvate this maximum occurred at 0.05 atmospheres O2, whilst in the absence of pyruvate the maximum occurred at 0.10 atmospheres O2. Malate, citrate, alpha-ketoglutarate, glucose and fructose were tested also, but none gave a similar effect to pyruvate. Addition of 14C-pyruvate and autoradiography indicated that exogenous pyruvate is metabolized through the interrupted Krebs cycle. These results are explained in terms of the activity of pyruvate: ferredoxin oxidoreductase and the ATP-induced oxygen sensitivity of nitrogenase.

Acetylene↗
PubMed1975

[Effect of blue and red light on the synthesis of ribosomal RNA in Chlorella].

In autotrophic cultures of Chlorella pyrenoidosa (strain 211-8b) incorporation of tritiated guanosine and uridine into ribosomal RNA is stimulated by light. Blue light of wavelengths around 457 nm is considerably more effective than red light around 679 nm (5-10(-10) Einstein cm-2 sec-1 for both). This effect can be demonstrated for young daughter cells (at the end of the dark period) and for older cells (at the end of the light period). It is shown to depend on a regulation of rRNA-synthesis. The blue light dependent enhancement of incorporation is more pronounced in the cytoplasmic rRNA (25 and 18 s) than in the chloroplast rRNA (23 and 16 s). Blue light of low intensity (1-10(-10) Einstein cm-2 sec-1) has nearly the same effectivity as the fivefold intensity, whereas red light of equal quantum fluxes enhances incorporation only slightly compared with the dark control. The blue light dependent enhancement of rRNA-synthesis continues in the following darkness in contrary to that caused by red light. This enhancement is also found in DCMU-poisened cultures. In contrast to this, is red light in presence of DCMU, incorporation into rRNA is nearly the same as in dark. It is concluded that the regulation of rRNA-synthesis in red light is closely connected to complete photosynthesis, while in blue light an additional regulation takes place independent of photosynthesis.

Chlorella↗
PubMed1992

Regulation of urea uptake in Pseudomonas aeruginosa.

The energy-dependent urea permease was studied in two strains of Pseudomonas aeruginosa, measuring the uptake (transport and metabolism) of 14C-urea. In both strains urea uptake in vivo and urease activity in vitro differed significantly with respect to kinetic parameters, temperature and pH dependence and response to metabolic inhibitors. Ammonium strongly interfered both with the expression of the urea uptake system and its activity. The inhibition of the uptake activity by ammonium was partially relieved by hydraziniumsulfate, which prevented the translocation of ammonium into the cell, and in a methylammonium/ammonium transport-defective mutant of strain DSM 50071. Furthermore, methionine-sulfoximine, which prevented the intracellular glutamine formation from ammonium via inhibition of glutamine synthetase, relieved the inhibition of urea uptake by ammonium. These findings suggested that urea uptake activity in P. aeruginosa is regulated by intracellular glutamine.

Amino Acids↗
PubMed1980

Inhibition of caffeine contractures of slow rat muscles by urea and its derivatives.

Contractures induced by rapid cooling of rat soleus muscles in the presence of low concentrations of caffeine (2-3 mmol.l-1) have been studied. Urea, methylurea and 1,3-dimethylurea inhibit reversibly these contractures as well as caffeine contractures (20 mmol.l-1, 30 degrees C) but do not affect twitches. This finding leads support to the idea of the existence of different mechanisms activating contraction in response to caffeine action or deplorization.

Animals↗
PubMed1993

Synthesis of oligosaccharides with oligoethylene glycol spacers and their conversion into glycoconjugates using N,N,N',N'-tetramethyl(succinimido)uronium tetrafluoroborate as coupling reagent.

Glycosides of glucose and lactose with di- and tetraethylene glycols, transformed into bifunctional (alcohol, ester) spacer molecules, have been synthesized. After deprotection, these spacer glycosides, containing a free carboxyl group, have been transformed efficiently into glycoconjugates using N,N,N',N'-tetramethyl(succinimido)uronium tetrafluoroborate (TSTU) for the formation of an active ester.

Ethylene Glycols↗
PubMed1992

Influence of chromium on some physiological variables of Anabaena doliolum: interaction with metabolic inhibitors.

The impact of 2,4-dinitrophenol and chlorophenyl dimethylurea on ATP content, carbon fixation, O2 evolution, nitrogenase activity and Cr uptake of Anabaena doliolum has been studied. 2,4-Dinitrophenol has been found to be more toxic than chlorophenyldimethylurea for all these processes. However, when Cr toxicity to above variables was assessed in their presence the interaction was less than additive. An initial (10-15 min) concentration-dependent rapid Cr uptake, followed by a slow one, indicates a biphasic uptake. A significant inhibition of Cr uptake in the presence of both these metabolic inhibitors suggests the involvement of metabolic processes in Cr uptake.

2,4-Dinitrophenol↗
PubMed1994

Denaturation behavior of alpha-chymotrypsinogen A in urea and alkylurea solutions: fluorescence studies.

The solvent denaturation of alpha-chymotrypsinogen (alpha-ctg A) in aqueous solution of urea, methyl-, N,N'-dimethyl-, ethyl-, propyl- and butylurea was studied by fluorescence measurements. Data were analyzed on the assumption of a two-state approximation to obtain the apparent equilibrium constant, Ku and the apparent Gibbs free energy of transition delta G0u. It has been observed that alkyl-substitution of urea significantly lowers the denaturant concentration needed to denature alpha-ctg A at 25 degrees C. Denaturation was accompanied by the red shift of emission maxima, the increase of the half-width of the fluorescence spectra, the increase of the fluorescence intensity, and the decrease of the fluorescence polarization. The differences of these fluorescence parameters observed for alpha-ctg A in alkylureas and urea can be ascribed to different unfolded states of the protein in different denaturant solutions. Minor differences in the extent of unfolding were confirmed by size-exclusion chromatography.

Animals↗
PubMed1995

Biological degradation of isoproturon, chlortoluron and fenitrothion.

For the purpose of biodegradation studies several microorganisms were isolated from soil and adapted under laboratory conditions in the presence of pesticides, with the following degradation results: isoproturon after 72 h-86%, chlortoluron after 72 h-93%, after 65 h-88% and fenitrothion after 72 h-66%. The cultures can be used for the biodegradation of pesticides in the lyophilized state with or without an organic carrier.

Bacteria↗
PubMed1994

Comparative toxicity of methyl isocyanate and its hydrolytic derivatives in rats. I. Pulmonary histopathology in the acute phase.

The present study describes the acute histopathological changes induced by methyl isocyanate (MIC) in the lungs of rats at 24 h after a single exposure to varied concentrations/doses of MIC by inhalation and subcutaneous (s.c.) routes and also delineates the effects due to the hydrolytic derivatives of MIC, viz., methylamine (MA) and N,N'-dimethyl urea (DMU). MIC, either inhaled or administered s.c., resulted in a wide range and extent of histopathological changes in the lungs, proportional to the exposure concentration/dose. The salient, effects of inhaled MIC are acute necrotizing bronchitis of the entire respiratory tract accompanied by varying degrees of confluent congestion, hyperemia and interstitial and intra-alveolar edema, while MIC administered s.c. led to prominent vascular endothelial damage, congestion and severe interstitial pneumonitis with apparently normal bronchial epithelium; and intra-alveolar edema only with the high dose. The only noteworthy lesion produced by MA and DMU (to some extent) was interstitial pneumonitis, suggesting their possible involvement in the subsequent inflammatory response of MIC. Except, for the endothelial changes, the overall spectrum of the histopathological lesions is quite comparable to those observed in the lungs of Bhopal victims during the acute phase.

Administration, Inhalation↗