Characteristics of maltose transporter activity in an ale and larger strain of the yeast Saccharomyces cerevisiae

Abstract

Kinetic studies on maltose uptake by ale and larger yeasts showed lower Km and higher Vmax values than for laboratory yeasts. Eadie-Hofstee plots were biphasic and inhibition by sulphydryl reagents was consistent with low affinity uptake by a specific transporter rather than by non-specific adsorption. High affinity maltose transport by both strains was inhibited by galactose, CCCP, 2, 4,-DNP and NEM. In contrast, glucose and pCMBS inhibited high affinity transport by the ale yeast but not by the larger yeast. In the case of pCMBS the difference could result from a single amino acid change in the maltose transporter.

Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease

“…Figure 4 shows the kinetics of the H ϩ -maltose symport activities of strain CEN.PK2-1C and strain LCM003 pregrown on maltose. As already extensively reported in the literature (7,27,32,42), the kinetics of maltose transport by the wild-type strain CEN.PK2-1C indicated the presence of both high-affinity (K m , ϳ5 mM) and low-affinity (K m , ϳ30 mM) transport activities. When the AGT1 gene was deleted from the genome, only the low-affinity H ϩ -maltose symport activity was affected (Fig.…”

“…All yeast ␣-glucoside transport systems so far characterized are H ϩ symporters that use the electrochemical proton gradient to actively transport these sugars into the cell, even for downhill transport (7,30,36). Maltose transport into the cell is required for the full induction of MAL genes, and several previous studies have also shown that maltose uptake is the rate-limiting step for fermentation (21,27,41).…”

Maltose Transport by Brewer's Yeasts in Brewer's Wort

“…Also glucose inhibited transport by the ale strain (K 1/2 = 150 mM) but not the lager strain. Crumplen et al 3 found the same for the ale and lager strain they studied, and reported a Ki of 95 mM for inhibition of the ale strain.…”

“…In addition, maltose and maltotriose compete for the same transporter in strains containing the AGT1-coded transporter, which carries several ␣-glucosides 8,24 , whereas glucose and maltose inhibit each other's transport in some strains, although they are not carried by the same transporters 3,23 . Jespersen et al 11 screened 5 ale yeasts and 25 lager yeasts and found that all contained MALx1 genes and all but one also contained AGT1 genes.…”

“…This is hard to explain if the maltose was taken up into the whole cytosol, but logical if it is restricted to the periplasmic space. Crumplen et al 3 showed that N-ethylmaleimide inactivates the low affinity systems of both a lager and an ale strain, suggesting that a protein with essential thiol is involved, which they believed to be a transporter. Fig.…”