Resistance to the peptide-like antibiotic negamycin in Escherichia coli

An $\text{Escherichia coli}$ mutant resistant to the peptide-like antibiotic negamycin carries a mutation, NEG40, which maps at minute 65 on the bacterial genome. Termination of protein synthesis, which is normally blocked by negamycin in wild type cellular extracts, continues with cellular extracts from the mutant in the presence of the drug; indeed, release of complete peptides from the polysomes still proceeds over a wide range of drug concentrations. The data suggest that the NEG40 mutation affects one of the components of the termination complex (ribosome or release factor).     

Effects of changes in circulating volume and in arterial pressure on plasma renin activity in the intact rat

The effects of changes in arterial pressure and in circulating volume on Plasma Renin Activity (PRA) in the intact rat were compared by two experimental procedures. Gradual volume depletion was induced by intraperitoneal injection of a hyperoncotic polyethyleneglycol solution (PEG) in absence of acute changes in Systolic Arterial Pressure (SAP). SAP was measured in the conscious state by the tail cuff technique. Plasma Protein Concentration (PPC) and Hematocrit (Hct) increases after PEG injection were compared as the index for measuring the Plasma Volume Reduction (PVR). PRA showed a significant (p less than 0.001) linear relationship with PPC, suggesting a direct dependence of renin secretion on volume depletion. Acute changes in the circulating volume were induced by controlled hemorrhages of 5.0, 10.0, 15.0 and 20.0 ml of blood/kg body weight. The increase in PRA showed a significant relationship with the changes in circulating volume, but it did not show any dependence on the changes in Mean Arterial Pressure (MAP). Our results suggest that, in the intact and conscious rat, renin secretion responds to the information from the cardiopulmonary volume receptors rather than to that from the high pressure receptors.     

Induction of the blue form of bacteriohodopsin by low concentrations of sodium dodecyl sulfate

The effects produced on bacteriorhodopsin by low concentrations of several detergents have been studied by absorption and fourth-derivative spectrophotometry. Sodium dodecyl sulfate induces the appearance of the blue form of bacteriorhodopsin (λ_max = 600 nm) at pH values up to 7.0 in a reversible manner. The apparent pK of the purple-to-blue transition raised with increasing concentration of SDS. Of the other detergents tested, only sodium dodecyl-N-sarcosinate showed a slight red-shift of the absorption band to 580 nm, whereas sodium taurocholate, Triton X-100 and cetyltrimethylammonium bromide did not favour the appearance of the blue form. The effect of SDS was found to be consistent with a localized conformational change that moves away the counter-ion of the protonated Schiff base.     

Instability of serum 17 beta-hydroxysteroid dehydrogenases of placental origin

The stabilization by glycerol of the serum estradiol 17 beta dehydrogenase has been investigated here in terms of time and temperature. The protected enzyme is stable for a month at least at --20 degrees C. Its activity reaches a maximum at 60 degrees C. In another connection, effect of reduced glutathione, of N. acetyl-cysteine and of various mineral ions on the enzymic conversion has been studied.     

Esters of trehalose from Corynebacterium diphtheriae: A modified purification procedure and studies on the structure of their constituent hydroxylated fatty acids

The purification procedure of 6,6′-diesters of trehalose from Corynebacterium diphtheriae was modified and the isolated substance was analysed by mass spectrometry as its permethylated derivative. The fatty acid moiety released from the glycolipid after alkaline hydrolysis was studied by mass spectral analysis of the O-methylated and O-acetylated methyl ester derivatives. By argentation thin-layer chromatography, three species of O-acetylated methyl esters were recognized, corresponding to saturated, mono-unsaturated and di-unsaturated α-branched-β-hydroxylated fatty acids. The double bond was located by ozonolysis of the O-acetylated methyl ester derivatives, by gas chromatography of the reaction product and mass spectrometry of the effluent from the gas chromatograph. The main components of each species of α-branched-β-hydroxylated fatty acids found in the gly colipid fraction of C. diphtheriae were 2-tetradecyl-3-hydroxyoctadecanoic acid (C₃₂H₆₄O₃, corynomycolic acid), 2-tetradecyl-3-hydroxy-11-octadecenoic acid (C₃₂H₆₂O₃, corynomycolenic acid), 2-tetradec-7′-enyl-3-hydroxy octadecanoic acid (C₃₂H₆₂O₃) and 2-tetradec-7′-enyl-3-hydroxy-11-octadecenoic acid (C₃₂H₆₀O₃, corynomycoldienic acid). The glycolipid fraction from C. diphtheriae is obviously a complex mixture of 6,6′-diesters of trehalose.     

Inhibition by cocaine of the baroreflex in the rat.

Sprague-Dawley rats were fitted under pentobarbital anesthesia with a catheter in the caudal artery and their carotid arteries were exposed. The pressure signal from the caudal artery was treated on line by a microcomputer for continuous display of blood pressure and heart rate measurements. The animals were administered intraperitoneally either 50 mg/kg of cocaine or an equal volume of saline. Five minutes later, stimulation of the baroreflex was performed by bilateral clamping of the two carotids for a period of 2 min. The same maneuver was repeated at 12, 24, and 31 min. Analysis of variance for repeated measures indicated that before carotid artery clamping, there was no significant difference between blood pressure measurements of the saline- and cocaine-treated groups. A two-factor analysis of variance of the repeated measures of the maximal variation in systolic pressure after each clamping showed a significant difference between control and cocaine-administered groups (P < 0.001), with the former displaying a much greater increment in blood pressure after carotid clamping. Cocaine exerts an inhibitory effect on the baroreflex that may be mediated through the increased angiotension II caused by the alkaloid.     

Implication of growth hormone in experimental induction of vitellogenesis by estradiol-17 beta in female silver eel (Anguilla anguilla L.)]

The effect of different preparations of growth hormone (GH) was assayed with 17 beta-estradiol on vitellogenesis in hypophysectomized or normal female silver eels. Vitellogenin (Vg) plasma levels were taken as the index of hepatic vitellogenesis. The E2 doses were chosen to give the same pattern for the plasma Vg level as in the controls. They decreased or remained undetectable in hypophysectomized or normal animals. GH also failed to induce alone a significant modification. When E2 was injected together with a GH, plasma Vg levels were 5.13 +/- 1.30 times higher with salmon GH in hypophysectomized eels and 2.01 +/- 0.25 times higher with bovine GH in normal eels. GH is shown to enhance the effects of E2 on hepatic vitellogenesis induction in a teleost.     

Metabolic behavior of acetyl glyceryl ether phosphorylcholine on interaction with rabbit platelets

The metabolic fate of 1-O-[³H]alkyl-2-acetyl-sn-glycero-3-phosphorylcholine ([³H]-AGEPC) upon interaction with rabbit platelets was investigated. [³H]AGEPC was converted to a product identified as the long-chain fatty acyl analog. The reaction was unaffected by extracellular calcium. After a lag time of 30 to 60 s the kinetics of the conversion was linear. The rate of the reaction was found to be a function of platelet and AGEPC concentrations. Of the [³H]AGEPC (10^?9m) 85 ± 5% was processed into the-long chain fatty acyl analog within 1 h when incubated at 37 2C with a 1.25 × 10⁹ platelets per milliliter suspension. A maximal number of 1200 to 3600 [³H]AGEPC molecules were converted to the long-chain fatty acyl derivative per minute per platelet in the presence of 2 mm EDTA. Under similar conditions the 1-O-[³H]alkyl-2-(lyso)-sn-glycero-3-phosphorylcholine ([³H]lysoGEPC) also was transformed to a comparable long-chain fatty acyl derivative at a much slower rate and to a lower extent. No significant increase in lysoGEPC was noted in incubation mixtures containing [³H]AGEPC. The possible direct transacylation of AGEPC upon interaction with platelets is discussed as well as the possible involvement of this reaction in directly triggering the platelet response to AGEPC stimuli.