Portable Device for Preparation and Delivery of Gas Mixtures

A simple, portable device for the preparation and delivery of gas mixtures has been designed and constructed. The basic feature of the device is the use of gas flow controllers to maintain stable flow rates over a wide range of downstream pressures, instead of the capillary tubes and water-filled barostats commonly used in gas-mixing devices. Elimination of the barostat avoids problems such as water leakage, the loss of gases through the barostat, and changes in gas pressure due to evaporative loss of water from the barostat. The absence of a barostat also provides a closed system, allowing the use of the device for mixing and delivering of toxic gases. The prototype of the device has been used to prepare mixtures of different gases for more than 1 year and has been found to operate consistently and reproducibly. The actual concentrations of O₂, CO₂, and N₂ in gas mixtures (determined by gas chromatography) immediately after mixing were between 2.2 and 6.6% of the desired values in four performance tests. Fluctuations in concentration of gases in mixtures after 9 days of continuous gas delivery was less than 2% in four performance tests.     

The effect of acute ethanol treatment on rates of oxygen uptake, ethanol oxidation and gluconeogenesis in isolated rat hepatocytes.

In hepatocytes isolated from fed rats, acute ethanol pretreatment (at a dose of 5.0 g/kg body wt.) did not change rates of O2 uptake. In cells from starved animals, acute ethanol pretreatment increased O2 uptake by 17-29%. The increased O2 uptake in hepatocytes from starved rats was not accompanied by increased rates of ethanol oxidation, but was accompanied by increased rates of gluconeogenesis under some conditions. The provision of ethanol (10 mM) as a substrate to cells from fed or starved rats decreased O2 uptake in the absence of other substrates or in the presence of lactate, and increased it in the presence of pyruvate or lactate and pyruvate. The results of this study show that the acute effects of ethanol on liver O2 uptake are dependent on the physiological state of the liver. Previously reported large (2-fold) increases in O2 uptake after acute ethanol pretreatment may have been an artefact owing to low control uptake rates (approximately 1.8 micromol/min per g wet wt. of cells) in the liver preparation used. The ATP contents (2.4-2.6 micromol/g wet wt. of cells) and rates of O2 uptake (2.5-5.0 micromol/min per g wet wt. of cells) of cells used in the present study were the same as values reported under conditions close to those in vivo. Therefore the increase in O2 uptake in cells from starved rats after acute ethanol pretreatment is likely to be of physiological significance.     

Using ontologies to describe mouse phenotypes

The mouse is an important model of human genetic disease. Describing phenotypes of mutant mice in a standard, structured manner that will facilitate data mining is a major challenge for bioinformatics. Here we describe a novel, compositional approach to this problem which combines core ontologies from a variety of sources. This produces a framework with greater flexibility, power and economy than previous approaches. We discuss some of the issues this approach raises.     

Olfactory sensitivity in tsetse flies: a daily rhythm

The diurnal tsetse Glossina morsitans morsitans bites especially in early morning and late afternoon; around midday feeding is at a low. In laboratory apparatus that measures the amount of locomotion under constant conditions over the photophase, the flies display a similar patterning of activity levels. The profile of daily rhythms for G. morsitans reported in the literature includes a number of motor and sensory motor systems that fluctuate cophasically. Lacking is a study on the patterning of the senses' response levels. In this paper we present the first instance of a daily modulation in the sense of smell. We stimulated the antennae with concentration series of host-derived odours and measured the spiking rate of cells at different times during the photophase. The concentration-response curves suggest that the sensitivity of antennal olfactory cells flows in parallel with the other daily rhythms. This was also reflected in electroantennograms (EAGs). The electroantennography was extended to G. fuscipes fuscipes, whose level of spontaneous locomotor activity--instead of following a U- shaped pattern--rises gradually over the photophase. Again, the EAGs appeared to parallel the species' locomotor activity. What we believe happens is that the organism tones down the sensitivity of its odour receptors during periods of anticipated inactivity for reasons of economy.      

Identification of proton transfer pathways in the X-ray crystal structure of the bacterial reaction center from Rhodobacter sphaeroides

Structural features that have important implications for the fundamental process of transmembrane proton transfer are examined in the recently published high resolution atomic structures of the reaction center (RC) from Rhodobacter sphaeroides in the dark adapted state (DQ_AQ_B) and the charged separated state (D⁺Q_AQ_B ^–); the latter is the active state for proton transfer to the semiquinone. The structures have been determined at 2.2 Å and 2.6 Å resolution, respectively, as reported by Stowell et al. (1997) [Science 276: 812–816]. Three possible proton transfer pathways (P1, P2, P3) consisting of water molecules and/or protonatable residues were identified which connect the Q_B binding region with the cytoplasmic exposed surface at Asp H224 & Asp M240 (P1), Tyr M3 (P2) and Asp M17 (P3). All three represent possible pathways for proton transfer into the RC. P1 contains an uninterrupted chain of water molecules. This path could, in addition, facilitate the exchange of quinone for quinol during the photocycle by allowing water to move into and out of the binding pocket. Located near these pathways is a cluster of electrostatically interacting acid residues (Asp-L213, Glu-H173, Asp-M17, Asp H124, Asp-L210 and Asp H170) each being within 4.5 Å of a neighboring carboxylic acid or a bridging water molecule. This cluster could serve as an internal proton reservoir facilitating fast protonation of Q_B ^– that could occur at a rate greater than that attainable by proton uptake from solution.     

The influence of some methodological factors on measurement of tryptophan oxygenase activities in crude homogenates of rat liver.

1. With two different methods for assaying the tryptophan oxygenase activity in rat liver homogenates, the effects of some methodological factors on the activity of the enzyme were studied. 2. In fed, but not in starved, rats a compound(s) absorbing at 365 nm, interfering with the reading of kynurenine absorbance, disappeared gradually during incubation. 3. A correction for this tryptophan-independent reaction was necessary in order to determine correct tryptophan oxygenase activity. 4. Blood remaining in liver tissue post mortem can serve as a source of cofactor haem for tryptophan oxygenase, causing spuriously high values for the activity of the holoenzyme form of tryptophan oxygenase. 5. A rapid and progressive activation of tryptophan oxygenase post mortem occurs in undisrupted liver tissue, and this activation is temperature-dependent.     

The binding of d-glucosyl-neoglycoproteins to the hepatic asialoglycoprotein receptor

The binding of D-glucosyl-neoglycoproteins and D-galactose-terminated glycoproteins to the hepatic asialoglycoprotein receptor of rabbit liver membranes were characterized and compared. The binding of both types of glycoproteins showed the same dependence on calcium concentration, sensitivity to neuraminidase, and degree of inhibition by various carbohydrate derivatives. These results, along with the observation that the rabbit liver membranes bound both the D-glucosyl- and D-galactosyl-terminated glycoproteins to the same extent, indicated that both types of glycoproteins bound to the same receptor. To confirm this hypothesis, receptors were isolated from rabbit livers by affinity chromatography using D-galactosyl-bovine serum albumin or D-glucosyl-bovine serum albumin immobilized on Sepharose. These receptors were shown to be identical by several chemical and immunological criteria as well as in their ability to bind equal amounts of D-galactosyl- and D-glucosyl-terminated glycoproteins. The conclusion is that the rabbit hepatic asialoglycoprotein receptor cannot discriminate between D-galactosyl and D-glucosyl-terminated glycoproteins and binds both.     

Effect of propranolol and cycloheximide on the ethanol-induced increase in liver tryptophan oxygenase activity in starved rats

Increased supply of tryptophan to the liver, resulting from the lipolytic action of ethanol, is suggested to be responsible for the increased activity of liver tryptophan oxygenase after ingestion of a single large dose of ethanol. This hypothesis was tested using an antilipolytic drug, propranolol, prior to ethanol treatment. It was found that, while propranolol did inhibit the ethanol-induced increase in blood unesterified fatty acids and free tryptophan concentrations, it did not prevent the activation of tryptophan oxygenase by ethanol. In another experiment, where cycloheximide was used to block protein synthesis, it was found that increased protein synthesis rather than decreased protein degradation is probably responsible for the accumulation of liver tryptophan oxygenase after ethanol ingestion.