Permeation of Glucose

A great deal of attention has been directed to the anaerobic fermentation by yeasts, notably Saccharomyces cerevisiae in its various forms (top and bottom brewers and bakers yeast). This has been industrially important, and the subspherical cells, about 6-8 /n in diameter, are produced under standard conditions. They can be brought into suspension with little or no clumping. They are then suitable for tests of the permeation through the surface of the suspended cells. From the discussion on pages 9-13, it follows that permeation can be treated either as the diffusion into spheres, where there is no semipermeable plasma membrane, or as the unidimensional diffusion through a relatively thin, slightly permeable membrane, with substantial complete diffusion of permeant. Since there is every reason to assume the latter case, the former case is considered unimportant. 

Slator and Sand (80), however, adopted the latter idea, f.e., there is no plasma membrane. A similar neglect of the plasma membrane occurs in the work of Krogh (41) and Gerard (24) noted on page 8. Slator and Sand concluded that the diffusion of glucose is about like that of mannitol 

Another effect by which permeability shows itself is evident during the be ning of fermentation, i.e., when yeast which has used up its store of carbohydrates is suspended in a glucose solution and measurements are begun forthwith. If permeability to glucose were very low, it is obvious that at first very little carbon dioxide would be produced, while later on it would be produced at a maximum rate. This situation is one of the disturbances in steady states discussed by Burton (8) (see page 7). But Biuinn s treatment is usable only for the simple case, S A B — Z, 

In fermentation no oxygen is used, so that there is no question as to permeability to oxygen. Glucose, provided in the medium, must permeate the yeast cell before metabolism starts. Metabolism, probably by means of several steps leads to the liberation of carbon dioxide presumably by decarboxylation. To be measured, this carbon dioxide must pass out through the plasma membrane and be freed as a gas from the medium (see Nord and Weichherz, 64). The very great permeability to carbon dioxide of all or most of all the studied types of plasma membrane leads to the conclusion that this step has no measurable influence. The liberation of carbon dioxide from even saturated solutions has been thought to require the use of special methods, such as the addition of large amounts of citric acid as Meyerhof advocates (53). Further study of this step is desirable. 

The intermediate steps of metabolism have been the subject of much discussion. Some aspects will be treated briefly below. Meyerhof (54) states that the glucose molecule passes anaerobically through twelve stable intermediary steps before forming alcohol and carbon dioxide at least three dissociable organic enzymes, twenty or more enzyme proteins and some bivalent metals (Mn and Mg) are necessary for the breakdown. This is a widely accepted conclusion from the work on fermentation by yeast extracts (press juice, maceration juice prepared from dried yeast, frozen yeast, or mechanically disrupted yeast) in which phosphoiylation is considered important in desmolysis. Decarboxylation of pyruvic acid appears to be the source of the carbon dioxide. Obviously then, carbon dioxide production is far from the initial step of permeation of glucose. 

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Glucose transporters are integral membrane proteins that catalyze the permeation of sugars into cells, along or against a concentration gradient. 

Secondary active uniport systems facilitating the permeation of a single solute, dependent on the electrochemical potentials of the solute molecules, are rare in bacteria. Only a glucose uptake system of Zymomonas mobilis has been studied in more detail [101]. 

Osmotic shock by rapid dilution of glucose makes ATP permeate through the bacterial membrane and glucose also acts as carbon source for ATP synthesis. The osmotic shock showed better reproducibility than authentic freeze-thaw treatment. Glucose could be replaced with other sugars when it is required. 

Two similar approaches were adopted by Ishihara et al. [364-368]. Membranes based on hydroxyethyl acrylate, dimethylaminoethyl methacrylate and trimethyl silyl styrene were solvent cast, and capsules containing insulin and glucose oxidase were prepared by interfacial precipitations. The authors reported dramatic changes in permeability in response to pH changes between 6.1 and 6.2. Moreover, addition of glucose induced an increase in the permeation rate of insulin, and upon removal of the glucose the permeability rates returned to their original levels. However, the conclusions were criticized [361] due to... 

The simplest of these functions is that of a permeability barrier that limits free diffusion of solutes between the cytoplasm and external environment. Although such barriers are essential for cellular life to exist, there must also be a mechanism by which selective permeation allows specific solutes to cross the membrane. In contemporary cells, such processes are carried out by transmembrane proteins that act as channels and transporters. Examples include the proteins that facilitate the transport of glucose and amino acids into the cell, channels that allow potassium and sodium ions to permeate the membrane, and active transport of ions by enzymes that use ATP as an energy source. 

T. Hofmann, On the preparation of glucose/glycine standard melanoidins and their separation by using dialysis, ultrafiltration and gel permeation chromatography, in Melanoidins in Food and Health, Vol. 2, J. M. Ames (ed), European Communities, Luxembourg, 2001, 11-21. 

H. Kimura H. Tama da, JapanP 68 19239(1968) CA 70, 59435u (1969) [Non-water-resistant slurry expls were changed to water-resistant by addn of carbohydrate syrup. In an example, the water permeation of an expl obtd by mixing AN 55, TNT 25, 3.2% aq soln of CM-ceilulose 15 and viscous liq (prepd by mixing with heating 70 parts glucose ... 

A is the surface area of a globule, R is the gas constant, T is the absolute temperature, g and c are the osmotic pressure coefficient and concentration of glucose, and subscripts 1 and 2 refer to the suspending fluid side and the compartment side of the oil layer. The water permeation coefficient of oil layer P0 is defined from "Equation 7", as follows ... 

When the concentration of glucose in the compartments is higher than that in the suspending fluid, an increase of the emulsion viscosity is observed. It is due to the increase of the volume fraction 4>w caused by the osmotic permeation of water across the oil layer. Using "Equation 10" one can obtain information on the water flux d /dt by measuring the changes in the viscosity of the W/O/W emulsion under an osmotic pressure gradient, so that the total extent of the oil layer in a unit volume of the sample, denoted as A, can be evaluated (see "Equation 8") by... 

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