In vivo and in vitro effects of boron on the plasma membrane proton pump of sunflower roots

The effect of boron excess and deficiency on H⁺ efflux from excised roots from sunflower ( Heliarahus annuus L. cv. Enano) seedlings and on plasma membrane H⁺-ATPase (EC 3.6.1.35) in isolated KI-washed microsomes has been investigated. When seedlings were grown in media with toxic levels of H₃BO₃ (5 m M ) or without added boron and exposed to light conditions, an inhibition of the capacity for external acidification by excised roots was observed as compared to roots from seedlings grown with optimal H₃BO₃ concentration (0.25 m M ). Toxic and deficient boron conditions also inhibited the vanadate-sensitive H⁺-ATPase of microsomes isolated from the roots. The mechanism of boron toxicity was investigated in vitro with microsorne vesicles. A strong effect of boron on the vanadate-sensitive, ATP-dependent H⁺ transport was found, but the vanadate-sensitive phospho-bydrolase activity was not affected. These results suggest that boron could exert an effect on the plasma membrane properties, directly or indirectly regulating, proton transport.     

One-step synthesis of Gly-Gly-PheNH2 from N-unprotected amino acid derivatives by papain in one-phase liquid media

Summary Papain was able to catalyze the one-step synthesis of Gly-Gly-PheNH₂, from N-unprotected amino acid derivatives. Maximum synthetic activity was obtained for a pH value of 6.5 and for a ]PheNH₂]/[Gly-GlyOEt] ratio of 6. The presence of an organic cosolvent, such as ethylene glycol, influenced the synthetic activity. Synthetic yield was higher than 65% for a 12.5 M cosolvent concentration.     

Kinetics of aerobic biodegradation of benzene and toluene in sandy aquifer material

Monod's equation adequately described aerobic biodegradation rates of benzene and toluene by the microbial population of a sandy aquifer when these compounds were initially present at concentrations lower than 100 mg/l each. Concentrations higher than 100 mg/l were inhibitory, and no benzene or toluene degradation was observed when these compounds were initially present at 250 mg/l each. The Monod coefficients were calculated as k = 8.3 g-benzene/g-cells/day and Ks = 12.2 mg/l for benzene, and k = 9.9 g-toluene/g-cells/day and Ks = 17.4 mg/l for toluene. Specific first-order coefficients would be 0.68 l/mg.day for benzene and 0.57 l.mg.day for toluene.     

Plasma determination of the novel anticonvulsant d,l-3-hydroxy-3-ethyl-3-phenylpropionamide and preliminary pharmacokinetic studies in the rat

A sensitive gas chromatographic method with flame ionization detection was developed for the analysis in plasma of the novel anticonvulsant d,l-3-hydroxy-3-ethyl-3-phenylpropionamide (HEPP), using d,l-2-hydroxy-2-ethyl-2-phenylacetamide as the internal standard. HEPP was extracted from alkalinized plasma into dichloromethane and quantified after derivatization with bis(trimethylsilyl)-trifluoroacetamide. Standard curves were linear from 0.5 to 50 and from 2 to 100 μg/ml of plasma, using 1.5 and 5 μg of the internal standard, respectively. The lower limit of detection at a signal-to-noise ratio of 3 standard deviations was 0.33 μg/ml of sample. The sensitivity, accuracy and reproducibility of the method were shown to be satisfactory for pharmacokinetic studies of HEPP. After intraperitoneal administration of 50 mg/kg to Wistar rats, the principal kinetic parameters were: absorption half-life = 0.04 h; volume of distribution = 1.32 l/kg; clearance = 4.40 ml/min; peak concentration = 50 μg/ml; peak time = 0.25 h; mean residence time = 4.55 h.     

Effects of eel (Anguilla anguilla L.) removals from selected sites of a stream on its subsequent densities

We assessed the effect of eel (Anguilla anguilla) removal from three sites of a Cantabrian stream upon its subsequent densities. In the first sample (Sept. 1986) numbers and densities were estimated as 43, 45 and 84 ind and 3490, 3030 and 3750 ind ha ⁻¹. Removal of these eels reduced the subsequent numbers and densities which, except on two occasions, were never reached again during the two years (eleven estimates) of study. Highest densities were recorded in the uppermost site in May and July, 1987, coincident with a strong drought and the lowest densities occurred in 1988 during a normal wet year. We hypothesize first that, because of a selective underground homing behaviour of eels, electro-fishing is inefficient and results in underestimates of the population. Second, seasonal variations of water discharge and droughts may not influence the homing behaviour of'eels until a threshold of dryness is reached. If this occurs, eels abandon their refuges and move towards the stream bottom. It seems that in Arroyo Chabatchos this threshold was exceeded in the summer of 1987 when the highest densities were estimated. The re-colonization of these sites experimentally depleted of eels, is a slow procces that lasts for, at least, two years.     

A K+-selective,three-state channel from fragmented sarcoplasmic reticulum of frog leg muscle

Summary Sarcoplasmic reticulum (SR) vesicles from frog leg muscle were fused with a planar phospholipid bilayer by a method described previously for rabbit SR. As a result of the fusion, K⁺-selective conduction channels are inserted into the bilayer. Unlike the two-state rabbit channel, the frog channel displays three states: a nonconducting (closed) state and two conducting states and . In 0.1m K⁺ the single-channel conductances are 50 and 150 pS for and , respectively. The probabilities of appearearance of the three states are voltage-dependent, and transitions between the closed and states proceed through the state. Both open states follow a quantitatively identical selectivity sequence in channel conductance: K⁺>NH ₄ ⁺ >Rb⁺>Na⁺>Li⁺>Cs⁺. Both open states are blocked by Cs⁺ asymmetrically in a voltage-dependent manner. The zero-voltage dissociation constant for blocking is the same for both open states, but the voltage-dependences of the Cs⁺ block for the two states differ in a way suggesting that the Cs⁺ blocking site is located more deeply inside the membrane in the than in the state.     

Spontaneous Mitotic Recombination and Evidence for an X-Ray-Inducible System for the Repair of DNA Damage in DROSOPHILA MELANOGASTER

Spontaneous mitotic recombination in the left arm of chromosome 3 was examined in both unirradiated control flies and sibs irradiated early in development by determining the sizes and frequencies of multiple-wing-hair (mwh) clones in the wing blade of heterozygous mwh/+ flies. Approximately 16% of the spontaneous mwh clones arise from events generating cells with normal division rates. The remaining 84% result from events generating cells with an average cell division rate one-third that of the surrounding cells; these are thought to result from events that generate aneuploid cells. Such clones probably arise from a failure correctly to repair spontaneous DNA damage. The frequency of spontaneous events late in development decreases significantly after irradiation as much as 150 hours earlier in development. The suppression of spontaneous events decreases with a longer period of time between irradiation and the final cell divisions in the wing blade. These results suggest the existence of a repair system for DNA damage in Drosophila that is induced by irradiation. The decrease in effect with time following irradiation could result from slow degradation or dilution by subsequent cell growth and division.