Changes in glutathione metabolic enzymes during yeast-to-mycelium conversion of Candida albicans

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Abstract
Candida albicans is a dimorphic yeast capable of producing alternate morphological forms (yeast or mycelium) in response to environmental changes. The intracellular level of glutathione, which helps to maintain the redox potential of the cell, is decreased significantly during the thermal induction of yeast-to-mycelium conversion. The reason for the decline of glutathione in the mycelial form is not understood. We have, therefore, investigated the levels of glutathione reductase, glutathione S-transferase, γ-glutamyltranspeptidase, and glutathione peroxidase, four key enzymes involved in glutathione metabolism, in the yeast and mycelial forms. Yeast cells of C. albicans 3153A were induced in Lee's medium (pH 6.5) at 37 °C for 3 h to produce germ tubes. Cell lysates were prepared from yeast and mycelial cells, and glutathione reductase, glutathione S-transferase, γ-glutamyltranspeptidase, and glutathione peroxidase were assayed spectrophotometrically. There was a 640% increase of the level of γ-glutamyltranspeptidase in the germ tubes as compared with the yeast cells. No other significant alteration of the levels of enzymes was noted. This increased activity of γ-glutamyltranspeptidase, which cleaves the glutamic acid residue of glutathione (Glu-Cys-Gly) appears to be, at least in part, responsible for the rapid decrease of the intracellular glutathione in C. albicans during the yeast-to-mycelium conversion.Key words: Candida albicans, dimorphism, glutathione, glutathione reductase, glutathione peroxidase, γ-glutamyltranspeptidase.