An examination was made of the effects of alterations in fatty-acyl unsaturation in the plasma membrane of Saccharomyces cerevisiae Y185 on the kinetics of accumulation of nine L-amino acids and L-trialanine (L-(Ala)3). Data revealed different kinetics only for L-threonine, L-histidine and L-(Ala)3 accumulation. Data for accumulation of L-threonine and L-(Ala)3 best fitted a model describing accumulation by one transport system, and for L-histidine, a model describing accumulation by one transport system and diffusion. Values for Vmax, but not KT, differed for L-threonine accumulation by oleyl as compared with linoleyl-enriched organisms whilst both KT and Vmax Values differed for accumulation of radioactively labelled L-(Ala)3. However, determination of L-(Ala)3 accumulation by the fluorescamine technique gave different results. Values for KT and the diffusion constant (D) but not Vmax, differed for L-histidine accumulation by oleyl-, palmitoleyl- or linoleyl-enriched organisms. Kinetic values for accumulation of L-aspartic acid, L-glutamic acid, L-leucine, L-isoleucine, L-valine, L-methionine and L-serine were however identical for organisms enriched in oleyl or linoleyl residues. When incubated in a glucose-containing phosphate buffer under conditions that led to derepression of the general amino-acid permease (GAP), Saccharomyces cerevisiae Y185 enriched in linoleyl residues more rapidly acquired GAP activity, as indicated by an increased ability to transport L-alanine, than did oleyl-enriched organisms. During derepression, KT values for the GAP were identical but Vmax values were greater for linoleyl-enriched organisms particularly after 1 h incubation in derepression buffer. The effects of linoleic-acid supplementation on removal of amino acids and peptides by Saccharomyces cerevisiae NCYC 240 during fermentation of brewer's all-malt wort, and peptides from an adjunct wort, were studied. In the former fermentations, the presence of linoleic acid have very little effect on amino acid or peptide removal but, in the latter, it appeared to speed up absorption of peptides by the yeast.
|Date of Award||1984|