Peptide uptake in yeast : glycolytic energy requirement and noninvolvement of external peptidase

Date Issued
March 1, 1980
Author(s)
Parker, David D.
Advisor(s)
J. M. Becker
Additional Advisor(s)
L. Huang
R. V. Miller
T. C. Montie
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Abstract
A fermentable energy source was required for the uptake of trimethionine by log phase cells of the yeast, Saccharomyces cerevisiae 139. The deletion of fermentable energy during uptake resulted in an eight-fold reduction in transport rate. Starvation of the cells under aerobic conditions resulted in an 80% loss of transport activity. This loss in activity was not reversed by treatment of cells with reducing agents. However, the loss of activity was prevented by starvation under a nitrogen atmosphere. Cells with a repressed mitochondrial system (e.g. glucose or anaerobically grown cells, petite mutants) had the greatest peptide transport capacity. In contrast, cells grown on an oxidizable energy source (e.g. glycerol, acetate) would not transport trimethionine, and cells grown on D-mannose, which is both fermented and oxidized, transported trimethionine but at a reduced rate. In addition, inhibitors of glycolysis such as arsenate or iodoacetic acid prevented transport. These data indicate that energy for peptide transport in S. cerevisiae is provided initially by glycolysis.

Recent studies showed that an external peptidase activity, aminopeptidase II, which hydrolyzes amino acid-p-nitroanilides and several di- and tripeptides is present in Saccharomyces cerevisiae. We have investigated the relationship between this peptidase activity and peptide transport in yeast. We found that intact cells of S. cerevisiae 139 hydrolyze amino acid-p-nitroanilides (PNA) by an activity similar to that of aminopeptidase Il. In contrast, intact cells of S. cerevisiae 139 did not hydrolyze trimethionine and the peptidase activity toward this substrate was localized in the soluble fraction of the yeast. These results and competition studies demonstrate that the external peptidase in S. cerevisiae 139 can Kinetic analysis showed that the Vmax for the intracellular hydrolysis of (Met)3 transport was 8.3 nmoles (Met)3 transported/min/mg dry wt. We conclude that this tripeptide is taken up by S. cerevisiae intact and rapidly hydrolyzed in the cytoplasm.

Degree
Doctor of Philosophy
Major
Microbiology
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