Product inhibition of immobilized Escherichia coli arising from mass transfer limitation.

Mass transfer-limited removal of metabolic products led to product-inhibited growth of Escherichia coli that was immobilized in a model system. Comparison of the growth kinetics of immobilized and free-living cells revealed no further physiological differences between cells in these two modes of existence beyond those manifested in the local concentrations of substrate and product. Bacteria were retained on a microporous membrane in a dense, planar aggregate and were grown anaerobically on a glucose-based minimal medium. Radioisotope labeling of the immobilized cell mass with 35S was used to determine growth kinetic parameters. Growth rates in the immobilized cell layer were measured by an autoradiographic technique which allowed comparison of the size of the growing region with the rate of cell convection caused by growth. Immobilized cell growth rates and growth yields ranged from near maximal (0.56 h-1 and 39 g of dry cell weight/mol of glucose, respectively) to substantially reduced (0.15 h-1 and 15 g/mol). The depression of these kinetic parameters was attributed to product inhibition arising from mass transfer-limited removal of acidic waste products from the cell mass. A simple one-dimensional reaction-diffusion model, which incorporated data on the product-inhibited growth kinetics of free-living cells collected in a product-limited chemostat, satisfactorily predicted product inhibition of immobilized cell growth.     

Semiautomated analysis of ethanol and acetate in human plasma by head space gas chromatography

Plasma samples (0.5 mL) were analyzed for ethanol and acetate by head space gas chromatography using a Porapak QS column (80-100 mesh). Acetate was esterified to methyl acetate simply by the addition of acidified methanol. The analytical ranges were 1.61-103 and 0.05-1.9 mM for ethanol and acetate, respectively. The within-run coefficients of variation did not exceed 4.7% for acetate and 2.7% for ethanol. After the oral administration of ethanol to two healthy human subjects, the concentration versus time profiles of plasma ethanol and acetate were determined. Acetate concentrations (0.4-0.9 mM) remained quite constant while ethanol was being metabolized and appeared not to be affected by the concentration of ethanol in the range 3-18 mM. The advantages of the method are speed and simplicity.     

Structure of the hepatitis A virion: peptide mapping of the capsid region.

Milligram amounts of highly purified hepatitis A virus (HAV) were obtained from persistently infected cell cultures. The HAV polypeptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose for detection by an enzyme-linked immunotransfer blot procedure. The HAV nucleotide-derived amino acid sequence was subjected to computer analysis to identify potential immunogenic regions within the HAV capsid polypeptides. Synthetic peptides corresponding to selected regions of each of the larger putative capsid polypeptides were coupled to keyhole limpet hemocyanin and used to immunize rabbits. Four of six anti-HAV peptide sera were strongly reactive. Antipeptide serum generated against amino acids (a.a.) 75 through 82 reacted with the 27,000-molecular-weight (MW) polypeptide; serum against a.a. 279 through 285 reacted with the 29,000-MW HAV polypeptide; and sera against a.a. 591 through 602 and 606 through 618 reacted with the 33,000-MW HAV polypeptide. These reactions enabled the identification of the gene order of the larger HAV P1 region gene products. Our data indicate the following molecular weights: HAV VP2 or 1B, 27,000; HAV VP3 or 1C, 29,000; and HAV VP1 or 1D, 33,000.     

A note on the production and use of antisera for the detection of part-digested sticklebacks in predator stomach-content samples

Preliminary experiments indicate that serological techniques provide a useful method of identifying specific prey antigens from the stomach contents of fish predators. Problems with cross-reacting antigens from different prey species can be reduced by absorbing anti-sera with tissue extracts of the cross-reacting species. Very small volumes of part-digested prey tissue are sufficient for identification of the prey species when using agarose diffusion plates (Ouchterlony tests).     

Increased loss and decreased synthesis of hepatic glutathione after acute ethanol administration. Turnover studies.

The effect of acute ethanol administration on rates of synthesis and utilization of hepatic glutathione (GSH) was studied in rats after a pulse of [35S]cysteine. A 35% decrease in hepatic GSH content 5h after administration of 4 g of ethanol/kg body wt. was accompanied by a 33% increase in the rate of GSH utilization. The decrease occurred without increases in hepatic oxidized glutathione (GSSG) or in the GSH/GSSG ratio. The rate of non-enzymic condensation of GSH with acetaldehyde could account for only 6% of the rate of hepatic GSH disappearance. The increased loss of [35S]GSH induced by ethanol was not accompanied by an increased turnover; rather, a 30% inhibition of GSH synthesis balanced the increased rate of loss, leaving the turnover rate unchanged. The rate of acetaldehyde condensation with cysteine in vitro occurred at about one-third of the rate of GSH loss in ethanol-treated animals. However, ethanol induced only a minor decrease in liver cysteine content, which did not precede, but followed, the decrease in GSH. The characteristics of 2-methylthiazolidine-4-carboxylic acid, the condensation product between acetaldehyde and cysteine, were studied and methodologies were developed to determine its presence in tissues. It was not found in the liver of ethanol-treated animals. Ethanol administration led to a marked increase (47%) in plasma GSH in the post-hepatic inferior vena cava, but not in its pre-hepatic segment. Data suggest that an increased loss of GSH from the liver constitutes an important mechanism for the decrease in GSH induced by ethanol. In addition, an inhibition of GSH synthesis is observed.     

The effects of putative amino acid neurotransmitters on somata isolated from neurons of the locust central nervous system

Changes in spike frequency, membrane potential and input resistance of somata freshly isolated from neurons in the metathoracic ganglia of adult locusts (Schistocerca gregaria) during bath and ionophoretic application of putative amino acid transmitters and analogues were studied using intracellular techniques. gamma-Aminobutyrate, glycine, taurine, cysteine and DL-ibotenate hyperpolarized the isolated soma, the response to kainic acid was depolarizing whereas L-glutamate and L-aspartate evoked a variety of potential changes. All of these compounds reduced the input resistance of the isolated soma. Ionophoretic studies showed that the receptors for L-glutamate and gamma-aminobutyrate are diffusely distributed over the somal surface.     

Locust nymphal neurones in culture: a new technique for studying the physiology and pharmacology of insect central neurones

A new technique for studying the physiology and pharmacology of locust central neurones is described. Somata isolated from neurones in the meso and metathoracic ganglia of third instar locusts (Schistocerca gregaria) were maintained for up to 4 weeks in co-culture (monolayer) with embryonic locust neurones. Most of the cultured cells became multipolar but a few were monopolar like their in vivo counterparts. They had diameters of 40-80 microns and "clean" (glial free) surface membranes. Cells 6-14 days in vitro were depolarized by acetylcholine and usually hyperpolarized by gamma-aminobutyrate, taurine and glycine. L-Glutamate and L-aspartate were inactive but further pharmacological studies are required to confirm this. Cultured larval neurones should provide excellent opportunities to study the molecular basis for drug-receptor interactions and voltage-sensitive membrane channels using the patch clamp technique.     

Comparison of health problems related to work and environmental measurements in two office buildings with different ventilation systems.

A cross sectional survey investigating "building sickness" was carried out in two buildings with similar populations of office workers but differing ventilation systems, one being fully air conditioned with humidification and the other naturally ventilated. The prevalence of symptoms related to work was assessed by a questionnaire administered by a doctor. A stratified, randomly selected sample of workers was seen (84% response). Building sickness includes several distinct syndromes related to work, most of which were significantly more common in the air conditioned building than the naturally ventilated building--namely, rhinitis (28% v 5%), nasal blockage and dry throat (35% v 9%), lethargy (36% v 13%), and headache (31% v 15%). The prevalence of work related asthma and humidifier fever was low and did not differ significantly between the two buildings. An environmental assessment of the offices was performed to attempt to identify possible factors responsible for the differences in the prevalence of disease. Globe temperature, dry bulb temperature, relative humidity, moisture content, air velocity, positive and negative ions, and carbon monoxide, ozone, and formaldehyde concentrations were all measured. None of these factors differed between the buildings, suggesting that building sickness is caused by other factors.