Yeasts amino acid utilization

With respect to the product, the solid sorbent can be neutral (placebo) or active. In the first case, the sorbent is used only as a carrier for heat-sensitive and otherwise hard-to-dry materials. Liquid bioproducts such as antibiotics, enzymes, yeasts, amino acids, and the Uke, which, when conventionally dried, can lose up to 70% of their biological activity, are typical examples. Sawdust, activated carbon, and ground straw or hay are typical solid carriers. After drying, the solid sorbent is either separated from the product or left as is for further utilization, as it is in the case of fodder antibiotics [17]. Figure 21.4 shows the co- and countercurrent modes of contacting solid carriers with liquid biomaterials in a spray dryer configuration. 

The manner in which amino acids are utilized by yeast has important implications in practical brewing. Thus when an amino acid is synthesized by the yeast from its carbon skeleton provided (from the same amino acid) in wort then the wort content of the particular amino acid will influence the metabolism of the yeast. Amino acids have therefore been classified according to the essential (i.e. not provided by carbohydrate metabolism) nature of their oxo-acid analogues in yeast metabolism. 

In Saccharomyces cerevisiae, as in most eukaryotic cells, the plasma membrane is not freely permeable to nitrogenous compounds such as amino acids. Therefore, the first step in their utilization is their catalyzed transport across the plasma membrane. Most of the transported amino acids are accumulated inside the yeast cells against a concentration gradient. When amino acids are to be used as a general source of nitrogen, this concentration is crucial because most enzymes which catalyze the first step of catabolic pathways have a low affinity for their substrates. 

He studied the synthesis and utilization of sulfur-containing compounds in man, rat, dog, goat, cow, ewe, bacteria, yeasts, cockroach, and algae, constantly being aware that the results are good only as the methods which were employed to obtain them. He devoted a great deal of his time to the development of better and more refined chemical and chromatographic methods for the isolation and determination of amino acids in proteins from a variety of sources, and he had even set up a laboratory in his house for the purpose, where he worked at all hours. 

Jiranek, V, Langiidge, P. Henschke, P.A. (1995). Amino acid and ammonium utilization by Saccharomyces cerevisiae wine yeasts from a chemically defined medium. Am. J. Enol. Vitic., 46, 75-83. 

Torrea-Goni, D.T. Ancin-Azpihcueta, C. (2001). Influence of yeast strain on biogenic amine content in wines Relationship with the utilization of amino acids during fermentation. Am. J. Fnol. Vitic., 52, 185-190. 

As with M. ruminantium, Methanobacterium strain MOH can utilize neither peptides nor amino acids as a nitrogen source replacing NH4 (Figures 5 and 7). NH4 utilization is essentially the same (Figure 8) when NH4 is the nitrogen source or when rumen fluid, amino acids, yeast extract, and Trypticase are present in the medium as complex sources of nitrogen that would be utilized in place of NH4 by most heterotrophic bacteria other than some rumen carbohydrate-fermenting anaerobes (11). 

Limited amino acid sequence information has shown that long-chain a-hydroxyacid oxidase from rat kidney is also related to these FMN-containing oxidoreductases (55). It is likely that several further members of this family remain to be identified. The flavodehydrogenase domain shows no sequence similarity to the lactate dehydrogenase from bacteria and higher eukaryotes that utilize NAD as a substrate. Yeasts lack such an enzyme and the substrate specificity of flavocytochrome 62 has presumably evolved independently of the NAD-linked dehydrogenases. 

Amino acid 78 and its y-glutamyl derivative are other components of the major pool of seleno compounds in accumulator plants, while selenomethionine (79) is the major compound in microorganisms like yeast, which is not specialized in selenium utilization. Se-Methylselenocysteine 5e-oxide (80), which is found in marine algae, tends to spontaneously decompose with the formation of pyruvate and ammonia via aminoacrylic acid and methaneselenic acid (81). The latter reacts with sulfhydryls or selenols to selenodisulfldes and diselenides. 

Site-directed mutagenesis was used to make additional amino acid substitutions at these sites in yeast ALS. At some of the sites, e.g. alall7, prol92, or trp586, nearly any substitution for the wild type amino acid that was tested resulted in a herbicide-resistant enzyme (Table I). Each of the mutant enzymes was characterized by enzyme assays to compare its activity, and its sensitivity to the sulfonylurea herbicide chlorimuron ethyl, to the wild type enzyme. These analyses have indicated that some of the mutations have little adverse effect on the activity of the enzyme, while decreasing sensitivity to the herbicide from three to greater than one thousandfold. The characteristics of these mutant enzymes were further evaluated in vivo in order to investigate the utility of particular herbicide/mutant enzyme combinations (Falco et al., manuscript in preparation). 

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