Activity and stability of Escherichia coli β-galactosidase in cosolvent systems

The kinetic parameters of E.coli -galactosidase were not altered by the addition of 2-propanol or ethyl acetate (1.6% v/v). While ethylene glycol (1.6% v/v) doubled the values of both KM (0.29 mM) and kcat (1393 s–), tetraethyleneglycol-dimethylether (Tetraglyme,1.6% v/v) preserved KM, but decreased kcat. At 50°C all the cosolvents dramatically shortened the enzymatic half life, and so did Tetraglyme and 2-propanol at 28°C. At 28°C, both ethyl acetate and ethylene glycol stabilised the enzyme 9- and 6-fold respectively. This fact, together with the activation effect of ethylene glycol may lead to practical applications. © Rapid Science Ltd. 1998     

Simultaneous determination of ethylene glycol, propylene glycol, 1,3-butylene glycol and 2,3-butylene glycol in human serum and urine by wide-bore column gas chromatography

A method has been developed for the separation and measurement of ethylene glycol and three other glycols (propylene glycol, 1,3-butylene glycol and 2,3-butylene glycol) in biological samples by wide-bore column gas chromatography with a flame ionization detector. The method used 1,3-propylene glycol (1,3-propanediol) as an internal standard. The method was linear at least from 2 to 1000 μg/ml, with a detection limit of 1 μg/ml. Analytical recoveries were 89–98% for the different concentrations. Precision studies showed coefficients of variation of 1.5–7.7% for the different concentrations. The assay was applied to the analysis of biological samples from two patients who had ingested ethylene glycol and/or other glycols in a suicide attempt.     

Autoradiographic demonstration of gastrin binding sites in rat gastric mucosa

The location of 125I-iodotyrosyl gastrin I binding sites in rat gastric mucosa was studied. Peptide specificity was demonstrated by competitive binding studies through the addition of a large dose of cold human gastrin I or cholecystokinin-octapeptide. Autoradiography of the stomach tissue was carried out by freeze-drying, embedding in Epon, wet-sectioning with ethylene glycol, and dry-mounting the emulsion film by means of the wire-loop method to prevent loss of the labeled substance. Specific binding sites for gastrin were found on parietal and chief cells, whereas few binding sites were seen on the surface mucous or mucous neck cells. Binding sites on the parietal cells were dispersed in the cytoplasm, while those on the chief cells were found near the basal plasma membrane.     

Survival of cultured cells and somatic embryos of Asparagus officinalis cryopreserved by vitrification

Cultured cells and somatic embryos derived from the mesophyll tissue of asparagus (Asparagus officinalis L.) were cryopreserved by vitrification. The vitrification solution (PVS) contains (w/v) 22% glycerol, 15% ethylene glycol, 15% propylene glycol and 7% DMSO in Murashige-Skoog medium enriched with 0.5M sorbitol. After initial cryoprotection with sorbitol supplemented MS medium containing 12% ethylene glycol, cells or embryos were exposed stepwise to 85% PVS at 0°C. They were loaded into 0.5 ml transparent straws, and were then plunged directly into liquid nitrogen. After rapid warming, PVS was removed and diluted stepwise. The highest survivals of vitrified cells and embryos were about 65 and 50%, respectively. Surviving embryos developed into plantlets.Abbreviations DMSO dimetyl sulfoxide - PVS vitrification solution - LN liquid nitrogen - DSC differential scanning calorimeter - MS Murashige-Skoog salt medium - NAA naphthalene acetic acid - BA 6-benzyladenine     

An environmental chamber for the study of the physiology of conventional and germ-free laboratory animals

The design and performance of a fully-climatized environmental chamber for the study of the physiology of conventional or germ-free research animals are described. The chamber temperature can be regulated between 14°–36°C ± 1°C, the humidity between 45–95 ± 2% at 14°C and between 20–95 ± 2% at 36°C. Bilaterally symmetrical lighting is variable over 15 stages between 50–2,400 lux. The performance of the chamber was evaluated in a trial study in which the effect of different chamber temperatures on the O₂-consumption of 24 conventional Sprague-Dawley rats held in groups of six to a cage with sexes separate. This showed a mean O₂-consumption at 14° to 16°C of 743 ml/(kg·hr), at 18° to 20°C of 653 ml/(kg·hr) at 26° to 28°C of 629 ml/(kg·hr) and at 30° to 32°C of 627 ml/(kg·hr). The differences between O₂-consumption at 14° to 16°C and 26° to 28°C and higher were significant (0.05 > p > 0.01).

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Zusammenfassung Konstruktion und Leistung einer vollklimatisierten Kammer zur Untersuchung physiologischer Reaktionen konventioneller sowie keimfreier Versuchstiere auf Umgebungseinflüsse werden beschrieben. Die Kammertemperatur kann zwischen 16° bis 36°C ± 1°C, die Feuchtigkeit zwischen 45–95 ± 2% bei 14°C und zwischen 20–95 ± 2% bei 36°C eingestellt werden. Die symmetrische Beleuchtung ist über 15 Stufen zwischen 0–2.400 Lux veränderlich. Die Eignung der Kammer wurde in einer Arbeit über den Effekt verschiedener Kammertemperaturen auf den O₂-Verbrauch bei 24 konventionellen Ratten Sprague-Dawley in Gruppen von sechs in einem Käfig nach Geschlechtern getrennt, geprüft. Der mittlere O₂-Verbrauch bei 14° bis 16°C war 743 ml/(kg·Std), bei 18° bis 20°C 653 ml/(kg·Std), bei 26° bis 28°C 629 ml/(kg·Std) und bei 30° bis 32°C 627 ml/(kg·Std). Die Unterschiede sind bei 14° bis 16°C und 26° bis 28°C und höher waren signifikant (0.05> p > 0.01).

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Resume On décrit ici l'agencement et le fonctionnement d'une chambre entièrement climatisée pour l'étude de la physiologie d'animaux conventionnels ou libres de germes. La température peut y être réglée à ± 1°C de 14° à 36°C et l'humidité peut y varier à ± 2% pris entre 45 et 95% à 14°C et entre 20 et 95% à 36°C. Des échairages symétriques placés de part et d'autre de la chambre peuvent êtres allumés selon 15 graduations différentes entre 50 et 2.400 lux. Le fonctionnement de la dite chambre a été mis à l'épreuve lors d'un essai de consommation d'oxygène par différentes températures. L'essai portait sur 24 rats conventionnels de la race Sprague-Dawley placés par groupes de 6 par cage en séparant les sexes. L'essai a montré une consommation de 743 ml/(kg·h) entre 14° et 16°C, de 653 ml/(kg·h) entre 18 et 20°C, de 629 ml/(kg·h) entre 26° et 28°C et de 627 ml/(kg·h) entre 30 et 32°C. La différence de consommation en O₂ est signifacative (0.05> p> 0.01) entre 14° à 16°C et 26° à 28°C ou davantage.

     

High-speed autoradiography of 3H-thymidine-labelled nuclei

Summary High-speed autoradiography with stripping film of ³H-thymidine-labelled cells was tested. The tests involved: (a) various times of immersion of emulsion-covered cell preparations in the mixture of dioxane-PPO-POPOP, at 20°C, (b) exposure of cell preparations and blanks for various times at either –70°C or +20°C, with different humidity levels. Autoradiographs of good quality could be produced by 2-min immersion in the scintillator, exposure time 1 h at either temperature and relative humidity 20–30%. A linear relationship between autoradiographic efficiency and exposure time of 1–7 h was found at either temperature, although the efficiency of autoradiographs exposed at –70°C was by approximately 30% higher than that of autoradiographs exposed at +20°C. Background values of autoradiographs dried with a fan and exposed for 1/4–7h at either –70°C or +20°C were 0.6–0.8 grain/100 m². Theoretical calculations and experimental data showed that high-speed autoradiographs are 30–50 times more efficient as compared with conventional stripping film autoradiographs, thus allowing a shortening of the respective exposure time. Theoretical aspects of efficiency and resolution of high-speed autoradiography are considered.This investigation was supported in part by MR II.1 grant. The technical assistance of Mrs. S. Bie is gratefully acknowledged     

Response surface optimization for the continuous glucose isomerization process

Production of fructose via a continuous glucose isomerization process was optimized using response surface methodology. Glucose isomerization was performed using immobilized glucose isomerase in a flow-through tubular reactor. Process factors eg pH (7.0–7.8), temperature (50–60°C), flow rate (5–17 ml min^–1) and glucose content (30–50% w/w) of the feedstock solution were simultaneously tested according to a central composite experimental design. Measured responses such as % isomerization, and fructose yield (gh^–1) has an excellent correlation with tested factors. The highest desirability,D, (geometric mean of % isomerization and fructose yield) was obtained when the feedstock (56–60°C) had 34–36% glucose, a pH of 7.4–7.8 and was pumped at 15 ml min^–1.     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Flexible non-nucleotide linkers as loop replacements in short double helical RNAs

Ethylene glycol oligomers have been studied systematically as non-nucleotide loop replacements in short hairpin oligoribonucleotides. Structural optimization concerns the length of the linkers and is based on the thermodynamic stabilities of the corresponding duplexes. The optimum linker is derived from heptakis (ethylene glycol) provided that the duplex end to be bridged comprises solely the terminal base pair; the optimum linker is derived from hexakis(ethylene glycol) if a dangling unpaired nucleotide is incorporated into the loop. Moreover, these linkers have been compared to other commonly used linker types which consist of repeating units of tris- or tetrakis(ethylene glycol) phosphate, or of 3-hydroxypropane-1-phosphate. In all cases, the correlation between linker length and duplex stability is independent of the kind of counter ions used (Na⁺, Na⁺/Mg²⁺, K⁺ or Li⁺). Furthermore, all duplexes with non-nucleotide loop replacements are less stable than those with the corresponding standard nucleotide loop. The results corroborate that the linkers are solvent-exposed and do not specifically interfere with the terminal nucleotides at the bridged duplex end.     

A cellulase-free xylanase from alkali-tolerantAspergillus fischeri Fxn1

Summary An alkali-tolerant fungusAsperqillus fischeri Fxn1 isolated from xylan enrichment grew in the pH range 5–10 and secreted an extracellular cellulase-free xylanase. Arabinose, lactose, maltose, cellobiose and glucose induced low levels of xylanase (1.8–9.0 IU/ml), whereas xylose, xylan and wheat bran induced higher level (34–45 IU/ml).CMcellulose and FPcellulose did not support growth. The optimum pH of xylanase was 6.0–6.5 and it was stable in a wide range of pH 5–9.5. The optimum temperature was 60°C and it was stable upto 55°C. The half-lives at 50 and 55 °C were 240 and 40 min. respectively. This enzyme released reducing sugars from pulp at pH 9.0 and 40°C.     

Influence of Volume of Nutrient Agar Medium on Development of Colonies of Marine Bacteria

Zusammenfassung Bei der Bestimmung der Anzahl Bakterien in frisch genommenen Seewasserproben mit dem Plattengußverfahren reduziert eine Agarmenge von über 10 ml die Anzahl sich entwickelnder Kolonien. Die erhaltenen Zahlen sind im allgemeinen am höchsten und die Ergebnisse am besten reproduzierbar, wenn genau 10 ml des Nähragars benutzt wird im Gegensatz zu unbestimmten Mengen zwischen 5 und 30 ml. Obgleich auch andere Faktoren eine Rolle spielen, wird der ungünstige Einfluß von Agarmengen, die merklich größer als 10 ml sind, in erster Linie den langsameren Abkühlungsraten während des üblichen Plattengußverfahrens zugeschrieben. Wenn Nähragar von 42° C bei Raumtemperatur (22–24° C) in Pyrex-Petrischalen gegossen wurde, kühlten 10 ml in ca. 1 min. auf 30° C ab, während 5 bis 24 min. gebraucht wurden, um Agarmengen von 20 bis 50 ml von 42° C auf 30° C abzukühlen. Viele marine Bakterien werden geschädigt, wenn sie Temperaturen ausgesetzt werden, die über 30° C liegen, wobei das Ausmaß der Schädigung von der Einwirkungszeit abhängt. Deswegen ist es überaus wichtig, daß der Agar vor dem Gießen auf 42° C gekühlt wird. Die Abkühlungsrate des Agarmediums in den Platten wird von der Beschaffenheit und der Temperatur der Tischoberfläche, auf der die Platten stchen, beeinflußt.

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Plating the heterogeneous bacteria occuring naturally in samples of raw sea water with volumes of molten nutrient agar exceeding 10 ml reduces the number of colonies which develop. Plate counts on replicate samples of sea water are generally highest and results are more nearly reproducible when 10 ml of nutrient agar is used rather than volumes ranging randomly from 5 to 30 ml. Although other factors are involved, the adverse effects of volumes of nutrient agar appreciable larger than 10 ml are attributed primarily to the slower cooling rates during conventional plating procedures. When nutrient agar medium at 42° C was poured into pyrex Petri dishes at room temperature (22–24° C), 10 ml of the medium cooled to 30° C in about one minute, whereas from about 5 to 24 minutes were required for 20 to 50 ml of the medium to cool from 42° C down to 30 ° C. Many marine bacteria are injured by being subjected to temperatures higher than 30° C, the extent of the injury being a function of time. Therefore, it is of paramount importance that agar be cooled to 42° C prior to pouring. The rate at which agar medium cools in plates is influenced by the composition and temperature of the table top on which the plates rest.

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Contribution from the Scripps Institution of Oceanography, University of California, La Jolla, California.     

Factors affecting the distribution, abundance and diversity of fishes of small, soft-substrata tidal pools within Moreton Bay, Australia

Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25 °C) covering the normal seasonal range in the lower Paraná river and Río de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight^–1 h^–1 at 15, 20 and 25 °C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg^–1 h^–1. Differences between sizes and between temperatures (except 15 vs. 20 °C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125–350 ml individual^–1 h^–1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Paraná watershed (up to over 200,000 ind m^–2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.     

Die Atmung beim KolibriAmazilia fimbriata während des Schwirrfluges bei verschiedenen Umgebungstemperaturen

Zusammenfassung An schwirrenden Kolibris (Amazilia fimbriata fluviatilis, mittleres Gewicht 5,7 g) wurden O₂-Verbrauch, CO₂-Produktion, Atemfrequenz, respiratorische Wasserabgabe und Flügelschlagfrequenz gemessen. Die Versuche wurden bei Temperaturen von 0–35 ° C durchgeführt.Der O₂-Verbrauch im Plug bei Temperaturen über 20 ° C beträgt 4,1 ml O₂/min= 43 ml O₂/g·h, was das 14fache des Basalstoffwechsels ist. Bei Erniedrigung der Umgebungstemperatur nimmt der O₂-Verbrauch kontinuierlich um etwa 6% je 10 ° C zu (Abb. 3). Es wird beim Schwirrflug eine weitgehende Substitution der thermoregulatorisch notwendigen Wärmeproduktion durch die bei der Kontraktion der Flugmuskeln entstehende Wärmemenge angenommen.Es wurde die Atemfrequenz mit rund 280/min bestimmt, das Atemzugvolumen mit 0,63 ml (BTS), die Ventilation mit 0,18 l/min (BTS) und die Sauerstoffausnutzung mit 2,2% errechnet.Die respiratorische Wärmeabgabe beträgt bei Temperaturen bis 20 ° C weniger als 20% der Wärmeproduktion, bei 35 ° C wurde das Maximum von 40% gemessen (Abb. 6). Bei trockener Luft macht die respiratorische Wasserabgabe 2,9–4,6% (0–20 ° C) bzw. rund 11% (bei 35 ° C) des Körpergewichtes pro Stunde aus. Bei 0 ° C gleichen sich Wasserproduktion durch Stoffwechselvorgänge und respiratorische Abgabe, bei allen anderen Temperaturen überwiegt die Abgabe: bei 35 ° C beträgt der Netto verlast 350% der Produktion.

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Respiration in the hummingbirdAmazilia fimbriata during hovering at different ambient temperatures

Summary In hovering hummingbirds (Amazilia fimbriata fluviatilis, mean weight 5.7 g) oxygen consumption, CO₂ production, breathing frequency, respiratory water loss and wing frequency were measured at various environmental temperatures from 0 to 35 ° C.The oxygen consumption above 20 ° C reached 4.1 ml/min = 43 ml/g·hr, and was 14 times the calculated basal rate. Oxygen consumption increased about 6% for a 10 ° C fall in environmental temperature (Fig. 3). During flight the thermoregulatory heat production at low temperatures was largely substituted by the heat that is produced by contraction of the wing muscles.The respiratory frequency was estimated to be 280/min, the tidal volume 0.63 ml (BTS), the ventilation 0.18 1/min (BTS) and the oxygen utilization as 2.2%.The respiratory heat loss at temperatures of 20 ° C and below was less than 20% of the heat production, while at 35 ° C a maximum loss of 40% was reached (Fig. 6). In dry air at 0–20° C the water loss measured 2.9 to 4.5% of body weight per hour while at 35 ° C the loss was 11%. At 0 ° C the respiratory water loss and metabolic water production were equal, but at all other temperatures the loss exceeded production (at 35 ° C the loss exceeded production by 350%).

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Herrn Prof. Dr. Jürgen Aschoff zum 60. Geburtstag gewidmet.

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N.R.C.C. Nr. 12844.     

Dehydrogenase enzyme histochemistry on freezedried or fixed resin-embedded tissue

Summary A method has been developed for the histochemical demonstration of a variety of dehydrogenases in freeze-dried or fixed resin-embedded tissue. Seven dehydrogenases were studied. Lactate dehydrogenase, NADH dehydrogenase and NADPH tetrazolium reductase were all demonstrable in sections of paraformaldehyde-fixed resin-embedded tissue. Freeze-dried specimens were embedded, without fixation, in glycol methacrylate resin or LR Gold resin at either 4°C or –20°C. All the dehydrogenases except succinate dehydrogenase retained their activity in freeze-dried, resin-embedded tissue. Enzyme activity was maximally preserved by embedding the freeze-dried tissue specimens in glycol methacrylate resin at –20°C. The dehydrogenases were accurately localized without any diffusion when the tissue sections were incubated in aqueous media. Addition of a colloid stabilizer to the incubating medium was not required. Freeze-drying combined with low-temperature resin embedding permits accurate enzyme localization without diffusion, maintenance of enzyme activity and excellent tissue morphology.     

Headspace solid-phase microextraction and gas chromatographic determination of dinitroaniline herbicides in human blood, urine and environmental water

Solid-phase microextraction (SPME) is a unique extraction and sampling technique, and it has been used for separation of volatile organics from water or other simple matrices. In this study, we have used SPME to separate dinitroaniline herbicides from complicated matrices of human urine and blood in order to broaden its application to biomedical analysis. The SPME conditions were optimized for water, urine and blood samples, in terms of pH, salt additives, extraction temperature, and fiber exposure time. Urine or water (1.0 ml) spiked with herbicides and 0.28 g of anhydrous sodium sulfate was preheated at 70°C for 10 min, and a polydimethylsiloxane-coated fiber for SPME was exposed to the headspace at 70°C for another 30 min; while spiked blood (0.5 ml) diluted with water (0.5 ml) was treated at 90°C in the same way. The herbicides were extractable under these conditions, and could be determined by gas chromatography–electron capture detector (GC–ECD). The recoveries of the herbicides, measured at the concentrations of 0.50 and 1.0 ng/ml urine or water, or 6.0 and 20 ng/0.5 ml blood, ranged from 35 to 64% for different herbicides from water or urine, and from 3.2 to 7.2% from blood. The headspace SPME yielded clean extracts of dinitroaniline herbicides from urine, blood or water, which could be directly analyzed by GC–ECD without further purification. The peak areas of the extracted herbicides were proportional to their concentrations in the range 0.1–10 ng/ml in water or urine, or 1–60 ng/0.5 ml in blood. The lowest detectable concentration of the herbicides lay in 0.1 ng/ml water or urine, or in 0.5 ng/0.5 ml blood. The intra- and inter-day coefficients of variation were within 14% for most of the analytes. Although the recoveries of the herbicides were rather low, the linearity of calibration curve and the precision were good. The developed method is more sensitive and much simpler in sample preparation than previously reported ones. With the established SPME method, a dosed herbicide was successfully separated and determined in rats' blood.     

Determination of diazolidinyl urea in a topical cream by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of diazolidinyl urea (DU) in a cream formulation is described. The aqueous phase of the emulsion was separated by centrifugation, removed, filtered, diluted and applied onto the HPLC system. DU was detected by ultraviolet absorption at a wavelength of 214 nm. The calibration curve was linear over the range of 79–553 μg/ml, and identical when determined on consecutive days. The relative standard deviation for repeat determinations was less than 0.5%. Recoveries were 97.74–101.72%. This analytical method is useful for quantitation of DU in cream formulations.     

Studies on the effects of climate on livestock production in Iraq

Measurements were made of the roughage and water intake of young Friesian cross males and females throughout a 12-month period. Results showed that the roughage consumption fell by 10–16% between the temperature range 11°–20°C and 21°–30°C and by 20–43% between the temperature range 11°–20°C and 31°–40°C. Water intake increased from 30–44% between 11°–20°C and 21°–30°C and by 45–92% between 11°–20°C and 31°–40°C.

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Zusammenfassung Rauhfutterverzehr und Wasserkonsum junger schwarzbunter Kreuzungsrinder wurden während eines Zeitraumes von zwölf Monaten gemessen. Die Ergebnisse zeigen, dass der Rauhfutterverzehr um 10–16% zurückging wenn die Lufttemperatur von 11°–20°C auf 21°–30°C stieg, und um 20–43% beim Anstieg von 11°–20°C auf 31°–40°C. Der Wasserkonsum nahm zwischen 11°–20°C und 21°–30°C um 30–44% und zwischen 11°–20°C und 31°–40°C um 45–92% zu.

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Resume Pendant une période de douze mois, on a cherché à mesurer la quantité d'eau et de foin consommée par un jeune bétail de race Friesian en Irak. Les résultats furent les suivants: Lors d'une augmentation de température de 11°–20°C à 21°–30°C, la consommation de foin diminua de 10 à 16%, allant même jusqu'à diminuer de 20 à 43% lors de températures augmentant de 11°–20°C à 31°–40°C. La consommation d'eau, quant à elle, augmenta de 30 à 44% dans le premier cas et de 45 à 92% dans le second.

     

Water and energy metabolism in the rock hyrax (Procavia habessinica)

Summary The influence of ambient temperature and water supply on water metabolism and O₂-consumption was measured in rock hyraxes (Procavia habessinica).With ad libitum food and water (control), water turnover rates of hyraxes were significantly lower than the general eutherian mean; water turnover rates were 61.4, 44.1 and 55.1 ml·kg^–0.82·24 h^–1 at 20, 27 and 35°C respectively. When greens were fed ad libitum but no drinking water was given, water turnover rate at 20°C was twofold higher, but at 27 and 35°C it was similar to that in control experiments.Water turnover rates were significantly reduced when no drinking water and only 25 g greens per day were offered (25.8, 22.0 and 29.3 ml·kg^–0.82·24 h^–1 at 20, 27 and 35°C respectively). Highest urine osmolality (3,200 mosm·kg^–1) was recorded at 20°C.Oxygen consumption under control conditions was 43% below that predicted on the basis of body weight for most eutherian mammals. The thermoneutral zone ranged from 27 to 35°C, and the basal metabolic rate was 165 kJ·kg^–0.75·h^–1.     

Improved enzymic digestibility of sugar cane bagasse following high temperature autohydrolysis

Summary Sugar cane bagasse was subjected to a two stage autohydrolysis treatment. In the first stage bagasse was heated in the presence of varying amounts of water at temperatures in the range 160–180°C to extract the hemicellulose fraction. The water insoluble residue was then heated in the presence of varying amounts of water at temperatures in the range 203 to 241°C. The effect of autohydrolysis on the digestibility of bagasse was assessed by hydrolysing the material with Trichoderma reesei cellulase enzymes (0.65 FPU/ml).     

The basal permeability to water of human red blood cells evaluated by a nuclear magnetic resonance technique

The characteristics of water diffusional permeability (P) of human red blood cells were studied on isolated erythrocytes by a doping nuclear magnetic resonance technique. In order to estimate the basal permeability the maximal inhibition of water diffusion was induced by exposure of red blood cells to p-chloromercuribenzene sulfonate (PCMBS) under various conditions (concentration, duration, temperature). The lowest values of P were around 0.7×10^–3 cm s^–1 at 10°C, 1.2×10^–3 cm s^–1 at 15°C, 1.4×10^–3 cm s^–1 at 20°C, 1.8×10^–3 cm s^–1 at 25°C, 2.1×10^–3 cm s^–1 at 30°C and 3.5×10^–3 cm s^–1 at 37°C. The mean value of the activation energy of water diffusion (E_a,d) was 25 kJ/mol for control and 43.7 kJ/mol for PCMBS-inhibited erythrocytes. The values of P and E_a,d obtained after induction of maximal inhibition of water diffusion by PCMBS can be taken as references for the basal permeability to water of the human red blood cell membrane.