Yeast permeability

Electroporation. When bacteria are exposed to an electric field a number of physical and biochemical changes occur. The bacterial membrane becomes polarized at low electric field. When the membrane potential reaches a critical value of 200—300 mV, areas of reversible local disorganization and transient breakdown occur resulting in a permeable membrane. This results in both molecular influx and efflux. The nature of the membrane disturbance is not clearly understood but bacteria, yeast, and fungi are capable of DNA uptake (see Yeasts). This method, called electroporation, has been used to transform a variety of bacterial and yeast strains that are recalcitrant to other methods (2). Apparatus for electroporation is commercially available, and constant improvements in the design are being made. 

In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP). However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4 -phosphopan-tetheine (Figure 45-18). The use of one multienzyme functional unit has the advantages of achieving the effect of compartmentalization of the process within the cell without the erection of permeability barriers, and synthesis of all enzymes in the complex is coordinated since it is encoded by a single gene. 

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. 

Mecfianism of Action An antifungai that binds with phospholipids in fungal cell membrane. The altered cell membrane permeability. Therapeutic Effect Inhibits yeast growth. 

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]. 

Morita, T., Iwamoto, Y., Shimizu, T., Masuzawa, T. Yanagihara, Y. (1989) Mutagenicity tests with a permeable mutant of yeast on carcinogens showing false-negative in Salmonella assay. Chem. pharm. Bull., 31, 407-409... 

Alcohol Sensor. On-line measurements of ethyl alcohol concentration in culture broth are required in fermentation industries. A microbial electrode consisting of immobilized yeasts or bacteria, a gas permeable Teflon membrane, and an oxygen electrode was prepared for the determination of methyl and ethyl alcohols(7). 

Physical and chemical genetic techniques have been used to enhance the permeability of yeast membranes. Permeabilizing agents, such as polymyxin B sulfate and polymyxin B nonapeptide, have been used to physically disrupt the integrity of yeast membranes (14). However, use of such chemical agents in drug screening is not ideal, because of the toxicity induced by polymyxin B treatment. 

Testing the Permeability (Sensitivity) of Yeast Strains SKY54 and SKY197 With Targeted Antifungals, and to a Diverse Chemical Library of Small-Molecular-Weight Compounds... 

Here, we have reported a general approach for creating a super-permeable yeast two-hybrid strain, and the application of this strain for HTS for identifi-... 

Boguslawski, G. (1985) Effects of polymyxin B sulfate and polymyxin B non-apeptide on growth and permeability of the yeast Saccharomyces cerevisiae. Mol. Gen. Genet. 199,401-405. 

The biggest concern over the use of recombinant microbes is that microbial cell walls constitute a permeability barrier for test compounds. Enzyme inhibitors that cannot accumulate in bacterial or yeast cytoplasm will appear as false nega-... 

Cell lysis under a high electric field is referred to as electroporation [6], Under these conditions, the cell membrane experiences dramatic changes in permeability to macromolecules. The main applications of the electroporation include the electrotransformation of cells and the electroporative gene transfer by the uptake of foreign DNA or RNA (in plants, animals, bacteria, and yeast). The electric field generates permeable microspores at the cell membrane, so that the nucleic acid can be introduced by electroosmosis or diffusion. 

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. 

V. V. Petrov and L. A. Okorokov (1990). Increase of the anion and proton permeability of Saccharomyces carlsbergensis plasmalemma by n-alcohols as a possible cause of its de-energization. Yeast, 6, 311-318. 

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