37] Sugar transport in normal and mutant yeast cells

Abstract

This chapter focuses on the sugar transport in normal and mutant yeast cell. Most studies of sugar transport in yeasts have been carried out with baker's yeast, Saccharomyces cerevisiae , which exhibits a variety of sugar transport processes––namely, facilitated diffusion, active transport, and, possibly, group translocation by transport-associated phosphorylation. The high- and low-affinity processes for monosaccharide uptake in S. cerevisiae may differ with respect to mechanism as well as kinetics. The low-affinity process is dearly due to a constitutive, facilitated diffusion mechanism; however, the high-affinity process may be mediated by a group translocation mechanism––namely, a transport-associated phosphorylation. Transport is customarily studied in washed cells suspended in distilled water or buffered salt solutions. Radiolabeled sugars are added to the cell suspensions, and samples are filtered and washed on glass microfiber or membrane filters. Glass microfiber filters are less expensive and allow much higher filtration rates than membrane filters.