SUMMARY: A comparison was made of kinetics of solute accumulation by NCYC 366 grown anaerobically under conditions that lead to enrichment of the plasma membrane with ergosterol and either oleyl or linoleyl residues. Values for and were identical for accumulation of -asparagine, -glutamine, HPO , Ca and SO , while for accumulation of -glucose, the value differed slightly but not significantly. Values for for accumulation of -lysine, by both the low-and high-affinity systems, decreased when oleyl residues were replaced by linoleyl residues. Under these conditions, values for the high-affinity system decreased while that for the low-affinity system increased. An Arrhenius plot for accumulation of lysine by the high-affinity system revealed a discontinuity when membranes were enriched in linoleyl residues. However, no discontinuity was evident on plots of lysine accumulation when membranes were enriched in oleyl residues. Similar plots for accumulation of -asparagine, which was used as a control, showed that substitution of linoleyl for oleyl residues significantly raised the transition temperature, but had little effect on the activation energy at temperatures below the discontinuity. When palmitoleyl residues were incorporated into the yeast plasma membrane, the value for -lysine accumulation by the high-affinity system was hardly altered, although the value was lowered, as compared with organisms with membranes enriched in oleyl residues. Replacement of oleyl by palmitoleyl residues lowered both the and values for accumulation of -asparagine. A modified statistical method is described for calculating confidence limits for transition points on Arrhenius plots.


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