Predictive modelling—or is it?

The Editors of Letters in Applied Microbiology will, at their discretion, publish invited and submitted 'Opinions' on subjects in the general area of Applied Microbiology. They will not be subjected to the normal refereeing procedures and reprints will not be provided. The 'Opinions' will not necessarily represent the views of the Society for Applied Bacteriology or of the Editors. The Editors may invite or readers may submit 'Responses' to published 'Opinions' provided that they are not merely polemics, and these will also be published at the discretion of the Editors. 'Responses' will be treated precisely like 'Opinions' . They should clearly indicate, in their first sentence, the 'Opinions' to which they are a response.     

1.5 MHz ultrasound irradiation of human lymphocytes.

Human lymphocyte cultures are exposed to 1.5 MHz continuous wave ultrasound, and it is demonstrated that cell death, as monitored by pyknosis, follows immediately on sonication at intensities within the usual therapeutic range (less than 1.7 W/cm2,spatial average). The number of cells affected is determined by the ultrasound intensity only, but the rate at which they proceed through their pyknosis cycle is modified by both the intensity and the duration of exposure. There is a clear indication of an intensity threshold for the effect approximately 1.1 W/cm2. Pulsed 1.5 MHz ultrasound (70 mus, 1 :1 pulses, 1.7 W/cm2 space-time average) results in a 15-20 hour delay in the measurable response to sonication. It is shown that the intracellular presence of a lysosomal-enzyme inhibitor strongly modifies the course of the ultrasound action. Evidence is presented to suggest that the basic interaction mechanism is via a cavitation process, but there are some difficulties with this interpretation, which are also discussed.     

Diethyl pyrocarbonate, a histidine selective reagent, inhibits estrogen binding to receptor protein in rat uterus cytosol

We find that at pH 6.1 diethyl pyrocarbonate inhibits estrogen binding to its receptor protein in rat uterus. Hydroxylamine partially reverses this inhibition and estrogen partially protects its receptor protein from this inhibition. We suggest that the estrogen receptor protein in rat uterus contains a nucleophilic site that either overlaps or is near the estrogen binding site. Based on the pH of inhibition reaction, the receptor concentration in the experiment, and the partial reversal of the inhibition by hydroxylamine, we suggest that this site contains a histidine residue or possibly an unusually reactive tyrosine residue that is important for estrogen binding.     

Adhesion of phospholipid vesicles to Chinese hamster fibroblasts: Role of cell surface proteins

The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) absorbed to the surfaces of EDTA- dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with[(3)H]DML or [(3)H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of two proteins with an approximately 60,000- dalton mol wt was particularly evident. Incubation of cells wit h (3)H-lipid vesicles followed by sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis showed that some of the (3)H-lipid migrated preferentially with these approximately 60,000-mol wt proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA- dissociated cells increased with decreasing temperatures. In contrast, cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. These results suggest two pathways for adhesion of lipid vesicles to the cell surface-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one. These findings are discussed in terms of current models for cell-cell interactions.     

Palaeolimnological studies of laminated sediments from the Shropshire-Cheshire meres

Studies of frozen and soft mud cores from Ellesmere Mere, Rostherne Mere and Berrington Pool, the three deepest of the Shropshire-Cheshire meres of the English Midlands, reveal the presence of laminations which may be varves. This hypothesis is being tested by means of fine resolution diatom and other microfossil analysis after the method of Simola (1977). Even where the laminations are faint and disrupted, it appears that seasonal signals from algal blooms are preserved.Organic geochemical analyses of sediments from Ellesmere show that the uppermost layers contain abundant organic matter (over 17% total dry matter) and that the extractable lipid fractions from different horizons exhibit clear compositional differences. These are produced by temporal changes in the organic inputs to the sediments, and also by diagnetic effects.The clastic and organic content of the cores also provides evidence for lake level variations in this area over the last 250 years.