Kinetic and Regulatory Properties of Yarrowia lipolytica Aconitate Hydratase as a Model-Indicator of Cell Redox State under pH Stress.

This paper presents an analysis of the regulation activity of the partially purified preparations of cellular aconitate hydratase (AH) on the yeast Yarrowia lipolytica cultivated at extreme pH. As a result of purification, enzyme preparations were obtained from cells grown on media at pH 4.0, 5.5, and 9.0, purified by 48-, 46-, and 51-fold and having a specific activity of 0.43, 0.55 and 0.36 E/mg protein, respectively. The kinetic parameters of preparations from cells cultured at extreme pH demonstrated: (1) an increase in the affinity for citrate and isocitrate; and (2) a shift in the pH optima to the acidic and alkaline side in accordance with the modulation of the medium pH. The regulatory properties of the enzyme from cells subjected to alkaline stress showed increased sensitivity to Fe2+ ions and high peroxide resistance. Reduced glutathione (GSH) stimulated AH, while oxidized glutathione (GSSG) inhibited AH. A more pronounced effect of both GSH and GSSG was noted for the enzyme obtained from cells grown at pH 5.5. The data obtained provide new approaches to the use of Y. lipolytica as a model of eukaryotic cells demonstrating the development of a stress-induced pathology and to conducting a detailed analysis of enzymatic activity for its correction.

Soluble Sugar and Lipid Readjustments in the Yarrowia lipolytica Yeast at Various Temperatures and pH.

Microorganisms cope with a wide range of environmental challenges using different mechanisms. Their ability to prosper at extreme ambient pH and high temperatures has been well reported, but the adaptation mechanism often remains unrevealed. In this study, we addressed the dynamics of lipid and sugar profiles upon different cultivation conditions. The results showed that the cells grown at various pH and optimal temperature contained mannitol as the major cytosol sugar alcohol. The elevated temperature of 38 °C led to a two- to three-fold increase in total cytosol sugars with concurrent substitution of mannitol for trehalose. Lipid composition in the cells at optimal temperature changed insignificantly at any pH tested. The increase in the temperature caused some drop in the storage and membrane lipid levels, remarkable changes in their composition, and the degree of unsaturated fatty acids. It was shown that the fatty acid composition of some membrane phospholipids varied considerably at changing pH and temperature values. The data showed a pivotal role and flexibility of the sugar and lipid composition of Y. lipolytica W29 in adaptation to unfavorable environmental conditions.