Sugars utilization

Hexokinase is of great biological interest since it would appear that not only in yeast cells but in most, if not all, plant and animal cells phosphorylation at C6 of the common hexoses D-glucose, D-fructose and D-mannose initiates sugar utilization. Since on solution in water the crystalline hexoses quickly undergo mutarotation, resulting in an equilibrium mixture of various tautomeric modifications, the fermentability... 

Type of hydrolyzate Sugar utilized, % Sugar recovered as lactic and acetic acids, %... 

Initially the reactor was fed at 92 mL/h (dilution rate of 0.29 Ir1) with P2 medium until there were visible signs of cell mass accumulation. It took about 5 d to accumulate cell mass and for the reactor to be productive. The flow rate was then increased to 100 mL/h, and the reactor was allowed to achieve a new steady state. At this stage, a control experiment was run and the reactor was fed with P2 medium. At this dilution rate (0.32 h1), the reactor produced 6.86 g/L of total ABE and 2.36 g/L of total acids (Table 1). This resulted in an ABE productivity of 2.19 g/(Lh) and a yield of 0.27. This productivity is manyfold higher than the productivity achieved in a batch reactor (0.38 g/[L h]) (10). Glucose utilization was 39.1% of that available in the feed (65.5 g/L). In these reactors, high productivity is achieved but at the expense of a low ABE concentration in the effluent as well as low sugar utilization. To improve sugar utilization, the reactor effluent should be recycled back to the reactor after ABE removal (11). 

To compare the performance of the reactor and evaluate the effect of CSL incorporation into the feed, the reactor was fed with CSL medium. Fermentation conditions and the dilution rate were kept constant as in Table 1 for the duration of this experiment. The reactor produced 6.29 g/L of total ABE, of which acetone, butanol, and ethanol were 2.00, 4.16, and 0.13 g/L, respectively (Table 1). This resulted in a productivity of 2.01 g/(L h) and a sugar utilization of 30.5% of that available in the feed (67.5 g/L). Compared to the control, the productivity was reduced by 10%. However, it is anticipated that it would be economical to use CSL compared with the P2 medium. This demonstrated that P2 medium can be replaced by economically available CSL. It is suggested, however, that the CSL... 

In certain instances, the exocellular and intracellular polysaccharides of yeasts have been used by taxonomists as an aid in classification of the parent organisms. For example, Lipomyces lipoferus may readily be distinguished from Lipomyces starkeyi by the sugars formed on partial and on complete hydrolysis of their exocellular polysaccharides (see Table VII), a differentiation that is difficult if morphological characteristics and sugar-utilization patterns are used. ... 

Previous sections presented approaches towards replacing the primary hydroxyl group at C-6 (hexoses) or C-5 (pentoses) with halides. These modified sugars are easily converted to unsaturated sugars utilizing reagents such as silver fluoride [79]. One early example, shown in Scheme 6.44, applies this chemistry to a glucose derivative. 

Another general approach leading to higher carbon sugars utilized acetylenic precursors [55, 58]. Conversion of an aldehyde into sugar acetylene was achieved using Corey s methodology [59] (PhsP/CBra, then a base). Treatment of the acetylene 56 with tributyltin hydride under the radical conditions afforded the -vinyltin 57 (O Scheme 27). 

Certain glycosides are hydrolyzed outside the plasmalemma. With this exception, the first step in sugar utilization is movement of the sugar across the plasmalemma, a process that generally occurs by means of a carrier associated with the plasmalemma. Without such carriers, the plasmalemma is impermeable to sugars.149 These carri-... 

Trombetta, E. S., and Helenius, A. (1999). Glycoprotein reglucosylation and nucleotide sugar utilization in the secretory pathway Identification of a nucleoside diphosphatase in the endoplasmic reticulum. EMBO J. 18, 3282-3292. 

Kuyper, M., Toirkens, M. J., Diderich, J. A., Winkler, A. A., Van Dijken, J. R, Pronk, J. T. (2005). Evolutionary Engineering of mixed-sugar utilization by a xylose-fermenting Saccharomyces cerevisiae strain. FEMS Yeast Research, 5, 925-934. 

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