Effects of hexavalent chromium on the plasma membranes of sensitive and tolerant mutants of Schizosaccharomyces pombe. An EPR study

Abstract

The interactions of chromium(VI) with the plasma membranes of chromium-sensitive ( chr-51S) and chromium-tolerant ( chr1–66T) mutants and their parental strain ( 6chr +) of a Schizosaccharomyces pombe strain were studied by electron paramagnetic resonance (EPR) spectroscopy. 5-doxylstearic acid (5-SASL) and 3-doxylbutyric acid (HO-185) spin probes were used to label the membranes. The order parameter S from the EPR spectra was calculated at different temperatures (0–25 °C) in order to characterize the internal dynamics of the membranes. In control experiments, both mutants exhibited differences in structural transitions in the both 5-SASL- and the HO-185-labeled membranes in comparison with their parental strain, suggesting differences in the membrane composition and/or rotational dynamics of these mutants. Addition of K 2Cr 2O 7 (225 μM) induced small decreases in the phase transition temperatures of the 5-SASL-labeled membranes of the parental and chromium-sensitive strains. More pronounced effects of the chromium compound on the HO-185-labeled membranes were detected as evidence that the membrane perturbations are mostly localized in the environment of the lipid–water interface.