Saccharomyces metabolic processes

Carman, G.M., and Henry, S.A., 1999, Phospholipid biosynthesis in the yeast Saccharomyces cerevisiae and interrelationship with other metabolic processes. Prog. Lipid Res. 38 361-399. Chang, H.J., 2001, Role of the unfolded protein response pathway in phospholipid biosynthesis and membrane trafficking in Saccharomyces cerevisiae. Department of Biological Sciences, Carnegie Mellon University. 

Feedback inhibition of amino acid transporters by amino acids synthesized by the cells might be responsible for the well known fact that blocking protein synthesis by cycloheximide in Saccharomyces cerevisiae inhibits the uptake of most amino acids [56]. Indeed, under these conditions, endogenous amino acids continue to accumulate. This situation, which precludes studying amino acid transport in yeast in the presence of inhibitors of protein synthesis, is very different from that observed in bacteria, where amino acid uptake is commonly measured in the presence of chloramphenicol in order to isolate the uptake process from further metabolism of accumulated substances. In yeast, when nitrogen starvation rather than cycloheximide is used to block protein synthesis, this leads to very high uptake activity. This fact supports the feedback inhibition interpretation of the observed cycloheximide effect. 

While unicellular fungi do not require metal transport systems, multicellular fungi and plants most certainly do, and we consider their transport in plants, and then consider how metal ions are sequestered in storage compartments before addressing their homeostasis. Once again, we consider in turn these processes for iron, copper, and zinc. Since iron metabolism has been most intensively studied in Saccharomyces cerevisiae, of all the fungi, we will focus our attention on iron homeostatic mechanisms however, as the reader will see shortly, copper and zinc homeostasis have many similarities. 

Two subunit FASs are also present in the palmitate synthase from Saccharomyces cerevisiae. These proteins form a multi-subunit complex, 06 6 and share active sites across the two subunits. The FAS proteins involved in primary metabolism in A. nidulans are shorter than HexA and HexB, used for formation of the hexanoyl CoA starter unit. Recent evidence suggests that the PKS is part of this protein complex (Figure 4B). The FAS/PKS complex (also called the NorS complex) has the stoichiometry a2P2Y2- Presumably hexanoylCoA never becomes a free unit and is transferred directly to the PKS by an internal trans thioesterification process. This explains why added precursor hexanoylCoA feeds poorly into a strain of Aspergillus in which HexA was inactivated. Furthermore, release of hexanoylCoA from the complex has not been found. 

The yeast responsible for alcoholic fermentation in winemaking is usually introduced into the must from the surface of the grapes, the surface of winery equipment, or from specifically prepared cultures. The fermentation process can occur either naturally, without inoculation, or by inoculating the must with selected starters. The use of locally selected yeast strains (usually belonging to the species Saccharomyces cereoisiae), with strain-specific metabolic characteristics can positively affect the final quality of the wine (Regodon et al., 1997 Romano et al., 2003). Several studies have clearly shown the effects of indigenous and inoculated yeast populations on the wine volatile composition (Mateo et al., 2001 Nurgel et al, 2003). 

Wine fermentations are never sterile and snpport a commnnity of microorganisms that changes over the life of the wine. Analysis of the impacts of the microbial commnnity on Saccharomyces has revealed the establishment of a novel prion state that restrnctnres the metabolism of this organism. The process of wine prodnction is nniqnely snited to the delineation of changing microbial dynamics and energy sonrce depletion. 

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