Manganese uptake and toxicity in magnesium-supplemented and unsupplemented Saccharomyces cerevisiae |
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Authors: | K J Blackwell J M Tobin S V Avery |
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Institution: | (1) School of Biological Sciences, Dublin City University, Dublin 9, Ireland, IE;(2) School of Biological and Molecular Sciences, Oxford Brookes University, Headington, Oxford OX3 OBP, UK. Fax: 01865 483242. e-mail: \SVAvery@Brookes.ac.uk, GB |
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Abstract: | The magnesium content of Saccharomyces cerevisiae was found to vary by up to fivefold at differing␣ stages of batch growth and during growth in the presence of differing magnesium
concentrations. Excess Mg was primarily sequestered in vacuoles. Mn2+-uptake experiments revealed that Mg-enriched cells had a markedly reduced capacity for Mn2+ accumulation. For example, after 6 h incubation in the presence of 50 μM Mn2+, Mn levels were approximately twofold higher in cells previously grown in unsupplemented medium than in those from Mg-supplemented
medium. These differences were further accentuated at higher Mn2+ concentrations and were not attributable to altered cell-surface charge or altered cell-surface Mn2+ binding. Cellular Mg status also influenced Mn toxicity towards S. cerevisiae. During exposure to 5 mM Mn2+, 50% reductions in the viability of cells with initial Mg contents of approximately 1400 and 2700 nmol (109 cells)−1 occurred after approximately 1.6 h and 3.6 h respectively. In cells containing 3300 nmol Mg (109 cells)−1, more than 75% viability was still maintained after 7 h incubation with 5 mM Mn2+. It is concluded that Mn2+ uptake and toxicity in S. cerevisiae are strongly influenced by intracellular Mg, possibly through Mg-dependent regulation of divalent-cation transport activity.
Received: 15 May 1996 / Received revision: 13 September 1996 / Accepted: 22 September 1996 |
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