Yeast cells permeability

In Saccharomyces cerevisiae, as in most eukaryotic cells, the plasma membrane is not freely permeable to nitrogenous compounds such as amino acids. Therefore, the first step in their utilization is their catalyzed transport across the plasma membrane. Most of the transported amino acids are accumulated inside the yeast cells against a concentration gradient. When amino acids are to be used as a general source of nitrogen, this concentration is crucial because most enzymes which catalyze the first step of catabolic pathways have a low affinity for their substrates. 

Catechins Yeasts Cell membrane Polyenes Stimulation membrane permeability increased intracellular catechin concentration [53]... 

The use of yeast cells as a eukaryotic complement to the Ames test led to the development of several protocols for the detection of mutation, gene conversion and recombination. The formal introduction of methods [23] followed by much development work from Zimmermarm s laboratory led to large systematic studies [24, 25] and OECD guidelines for the test battery (OECD 480, 481). However the assays are now rarely used, at least in part because of concerns over low sensitivity, thought to reflect limited permeability of the cell wall. 

An early example of an MIP-QCM sensor was a glucose monitoring system by Malitesta et al. (1999). A glucose imprinted poly(o-phenylenediamine) polymer was electrosynthesized on the sensor surface. This QCM sensor showed selectivity for glucose over other compounds such as ascorbic acid, paracetamol, cysteine, and fructose at physiologically relevant millimolar concentrations. A unique QCM sensor for detection of yeast was reported by Dickert and coworkers (Dickert et al. 2001 Dickert and Hayden 2002). Yeast cells were imprinted in a sol-gel matrix on the surface of the transducer. The MIP-coated sensor was able to measure yeast cell concentrations in situ and in complex media. A QCM sensor coated with a thin permeable MIP film was developed for the determination of L-menthol in the liquid phase (Percival et al. 2001). The MIP-QCM sensor displayed good selectivity and good sensitivity with a detection limit of 200 ppb (Fig. 15.7). The sensor also displayed excellent enantioselectivity and was able to easily differentiate the l- and D-enantiomers of menthol. 

Ergosterol, the predominant sterol in yeast cells, plays an important role in membrane fluidity, permeability and the activity of many membrane-bound enzymes. In terpene-treated cells, ergosterol synthesis was strongly inhibited, and a global upregulation of genes associated with the ergosterol biosynthesis pathway was described in response to terpene toxicity [80, 121]. 

An important harmful effect of metals at the cellular level is the alteration of the plasma membrane permeability, leading to leakage of ions like potassium and other solutes (Passow and Rothstein, 1960 Wainwright and Woolhouse, 1978 De Filippis, 1979 De Vos et al., 1988, 1991). After supply of copper ions Ohsumi et al. (1988) demonstrated for yeast cells and De Vos et al. (1989) for root cells of Silene cucubalus that the permeability barrier (controlled by means of potassium leakage) of the plasma membrane was almost immediately lost. Oshumi et al. (1988) also reported a quick release of amino acids, especially glutamate and aspartate. After McBrien and Hassall (1965) and Overnell (1975), who studied potassium release from algal cells, the increased permeability of the plasma membrane may be considered to constitute the primary toxic effect of copper. 

Since MASPIT is a simple binding assay, it could also be used potentially to screen small molecule libraries for compounds that interfere with or compete for binding of a known molecule with its target protein. Therefore, MASPIT provides an opportunity for small molecule discovery that is not possible with Y3H (due to the less favorable permeability of yeast cells to small molecules). 

The subscripts on the usual process parameters indicate the positions in the process to which these parameters refer. The kinetics of yeast growth can be described by a Monod rate expression with = 0.625 h and Kg = 2 g/L. Cell death and cell maintenance effects are negligible, as is formation of products other than yeast cells. The yield coefficient x/s is 0.44. The effluent from the bioreactor flows directly to a membrane filtration apparams. The membrane is completely permeable to the substrate, so the concentrations of the substrate in the CSTBR, the effluent from the bioreactor, and the permeate from the membrane and in the recycle stream are all identical. The membrane rejects a substantial proportion of the yeast cells so that the ratio of the concentration of yeast in the recycle stream is a factor of 4 larger than that in the effluent from the CSTBR. Volumetric expansion and contraction effects may be considered negligible. 

The point at which the fungal cell can be considered dead is debatable [297]. It is not possible to reverse the lethal action of polyenes once sufflcient antibiotic molecules have combined with the cell membrane. Lethal levels of nystatin brought glycolysis of S. cerevisiae to a halt within 40 min [298] and 95% of the yeast cells were not viable after 30 min. Cell death inevitably follows destruction of membrane permeability. Whether the observed changes in cell metabolism, composition or morphology are causes or symptoms of death is unclear the sequence of antibiotic action in organisms other than fungi has received little attention. 

Although the catalytic activity of T. brassicae CGMCC0574 whole cells in the enantioselective hydrolysis of ketoprofen ester was initially moderate, it was significantly promoted after the cells were pretreated for a few hours in a buffer containing an alcohol as the modulator. This suggested a possible permeability barrier from the cell membrane against the mass transfer of substrates and/or products. Therefore, the permeabilization of the yeast cells was considered to be favorable for the enzymatic resolution of ketoprofen. 

The yeast cell membrane may be envisioned as a selectively permeable barrier that serves a vital role in the organism s ability to maintain osmotic balance and regulate transport of essential nutrients into and metabolites (including ethanol) out of the cell. Ethanol is soluble in both aqueous and lipid phases of the cell membrane and its formation and passive effusion eventually interferes with structure and function of the membrane. Particularly important in this regard are the cell-membrane-associated transport enzymes such as those responsible for uptake of sugars and critical amino acids. During active fermentation at warm temperatures, ethanol accumulates intracellularly faster than it can be eliminated from the cell. This situation worsens as extracellular concentrations increase. Thus, temperature- and ethanol-directed inhibition is likely the result of the time delay arising from passive diffusion coupled with impaired membrane function. 

Both brewer s and baker s yeast cause a localized oedema when injected into the rat paw [13, 273, 303, 357, 507, 558, 687]. Moreover, yeast and its active component mannan elicit a generalized reaction when injected parenterally [81, 273]. PoYSER and West [503] have shown that mannan [493, 494] and zymosan [501], both yeast cell-wall polysaccharides, increase vascular permeability when injected intradermally. Yeast mannan (a mannose polymer) was about 20 times more active than dextran in this respect, and the possibility that their relative activity depends on the ratio of certain side-chain to main-chain was suggested. 

R. H. PoYSER and G. B. West, Changes in Vascular Permeability Produced in Rats by Dextran, Ovomucoid and Yeast Cell Wall Polysaccharides, Br. J. Pharmac. Chemother. 25, 602-609 (1965). 

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