Computer-assisted nonlinear regression analysis of the multicomponent glucose uptake kinetics of Saccharomyces cerevisiae.
The kinetics of glucose uptake in Saccharomyces cerevisiae are complex. An Eadie-Hofstee (rate of uptake versus rate of uptake over substrate concentration) plot of glucose uptake shows a nonlinear form typical of a multicomponent system. The nature of the constituent components is a subject of debate. It has recently been suggested that this nonlinearity is due to either a single saturable component together with free diffusion of glucose or a single constitutive component with a variable Km, rather than the action of multiple hexose transporters. Genetic data support the existence of a family of differentially regulated glucose transporters, encoded by the HXT genes. In this work, kinetic expressions and nonlinear regression analysis, based on an improved zero trans-influx assay, were used to address the nature of the components of the transport system. The results indicate that neither one component with free diffusion nor a single permease with a variable Km can explain the observed uptake rates. Results of uptake experiments, including the use of putative alternative substrates as inhibitory compounds, support the model derived from genetic analyses of a multicomponent system with at least two components, one a high-affinity carrier and the other a low-affinity carrier. This approach was extended to characterize the activity of the SNF3 protein and identify its role in the depression of high-affinity uptake. The kinetic data support a role of SNF3 as a regulatory protein that may not itself be a transporter.
Coons
D M
DM
Department of Viticulture and Enology, University of California, Davis 95616-8749, USA.
Boulton
R B
RB
Bisson
L F
LF
D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D004058:Diffusion; D005656:Fungal Proteins / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D012044:Regression Analysis; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D012984:Software
D005656:Fungal Proteins; D009004:Monosaccharide Transport Proteins; D003847:Deoxyglucose; D005947:Glucose