Urea transport-defective strains of Saccharomyces cerevisiae

Abstract

Experiments characterizing the urea active transport system in Saccharomyces cerevisiae indicate that (i) formamide and acetamide are strong competitive inhibitors of urea accumulation, (ii) uptake is maximal at pH 3.3 and is 80% inhibited at pH 6.0, and (iii) adenosine 5'-triphosphate generated by glycolysis in conjunction with formation of an ion gradient is likely the driving force behind urea transport. Mutant strains were isolated that are unable to accumulate urea at external concentrations of 0.25 mM. These strains also exhibit a depressed growth rate on 10 mM urea, indicating existence of a relationship between the active transport and facilitated diffusion modes of urea uptake. Urea transport in Saccharomyces cerevisiae may occur by two routes (5). The first mode is a

Ethyl Carbamate in Fermented Beverages: Presence, Analytical Chemistry, Formation Mechanism, and Mitigation Proposals

“…Because urea reabsorption can decrease EC levels, considerable efforts should be made to explore this phenomenon. Based on the environmental urea concentration, the urea import pathway is commonly divided into 2 mechanisms (Cooper and Sumrada ; Sumrada and others ). When the extracellular concentration of urea is higher than 0.5 mmol/L, it enters the cell via a facilitated diffusion system that is energy‐independent and encoded by the DUR4 gene.…”

Functional enhancement of Sake yeast strains to minimize the production of ethyl carbamate in Sake wine

“…Yeast can import urea in one of two ways, depending on environmental urea concentration (Cooper and Sumrada 1975;Sumrada et al 1976). At high extracellular concentrations (>0AE5 mmol l )1 ), urea enters the cell in an energy-independent fashion via a facilitated diffusion system encoded by the DUR4 gene.…”

“…At high extracellular concentrations (>0AE5 mmol l )1 ), urea enters the cell in an energy-independent fashion via a facilitated diffusion system encoded by the DUR4 gene. At low concentrations (K m = 14 lmol l )1 ), urea is imported via a 735 amino acid, integral membrane, ATP-dependent sodium-urea symporter, which is encoded by the NCR-sensitive DUR3 gene (Cooper and Sumrada 1975;Sumrada et al 1976). In addition to its role as a urea importer, DUR3 has been shown to regulate intracellular boron concentration (Nozawa et al 2006); however, a clear physiological role for DUR3 has yet to be defined.…”

A second nitrogen permease regulator in Saccharomyces cerevisiae

“…Two systems of saturable urea transport have been described [1]: one is a low-affinity facilitated transporter (Km 1 mM), the other being a high affinity active transport system (Kin 14/tM). A mutant affected in this active transport [4] has enabled the cloning of a gene located on chromosome VIII, DUR3, coding for a putative trans-membrane protein which is necessary for a functional active transport to be present [5]. There is no direct demonstration of the DUR3 protein being the urea carrier, and authors agree that other proteins could be involved in the transport mechanisms, for instance in the coupling of the urea carrier with an energy source.…”