Magnesium ions yeast

Larsen, T.M., Wedeking, J.E., Rayment, I. and Reed, G.H. (1996) A carboxylate oxygen of the substrate bridges the magnesium ions at the active site of enolase structure of the yeast enzyme complexed with the equilibrium mixture of 2-phosphoglycerate and phosphoenolpyruvate at 1.8 A resolution, Biochemistry, 30, 4349-4358. 

Yeast hexokinase (1-2 international units per mL reaction solution) acting for 20 min in the presence of 10 mM D-glucose has proven to be quite effective in depleting ATP at levels not exceeding 1 mM. At pH 7 in the presence of 1-2 mM uncomplexed magnesium ion, the equilibrium constant for the hexokinase reaction is about 1500 thus, one can anticipate substantial conversion of 1 mM ATP, as indicated by the following equation ... 

Figure 6.3 shows the time course of ethanol production as a function of feed composition (Table 6.3). The best feed solution was feed D which permitted the bed to run for eight hours without quenching and resulted in a higher ethanol yield (0.46) than feed A (0.35) which contained only glucose. Potassium and magnesium ions are known to stimulate fermentation (Jones and Greenfield, 1984 Maynard, 1993). Feed C caused the bed to quench after only two hours because, under anaerobic conditions, the yeast extract supplied was unable to be assimilated sufficiently quickly and the remainder was therefore... 

Figure 13-2 View of the active site of yeast enolase containing a bound molecule of 2-phospho-D-glycerate. The catalytic magnesium ion is at the left but the "conformational" metal is not visible here. The imidazole group of His 159 serves as the catalytic base and the -NH3+ of Lys 396 or Lys 34573b as the catalytic acid. From Vinarov and Nowak.69...

The importance of magnesium ions for the catalytic activity of the yeast PDC was recognized in 1931 by Lohmann and Schuster [30]. One year later, Auhagen [31] isolated a further thermostable substance, cocarboxylase , which was necessary for the decarboxylation of pyruvate. In 1937, Lohmann and Schuster [32] investigated the constitution of cocarboxylase and found it to be a diphosphate ester of vitamin B1 (ThDP) 3 (Scheme 2). Three years later, Green and co-workers [33] proposed that magnesium functions as a bridge ... 

Friederich, M. W., and Hagerman, P. J. (1997). The angle between the anticodon and aminoacyl acceptor stems of yeast tRNA(Phe) is strongly modulated by magnesium ions. Biochemistry 36, 6090—6099. 

An enzyme closely related to the aldolases is transketolase. The enzyme is commercially available (from baker s yeast) and can also be obtained from spinach leaves. Transketolase catalyses the stereospecific synthesis of C—C bonds using aldehydes as the electrophiles, with a suitable 2-carbon ketol donor [e.g. hydroxypyruvate (9)] as the nucleophile (Scheme 5.11). The use of hydroxypyruvate ensures that the reaction goes to completion, since carbon dioxide is evolved as the by-product, and hence the reaction is irreversible. In addition, both magnesium ions and catalytic thiamine pyrophosphate are required as co-factors. 

In an X-ray analysis of the yeast tRNA , a specific magnesium-binding site in the vicinity of a G4-U69 wobble base pair was foimd. Thus it seemed attractive to study if a G-U pair is a specific binding site for magnesium ions. Addition of the diamagnetic Mg " cation has only little, though measurable, effects on the chemical shifts of the imino resonances (< 0.05 ppm). Since it is known from a number of biological and biochemical studies that... 

The effect of medium components on the production of succinic acid by A. succiniciproducens was systematically studied. Sodium ion is essential for glucose transport, and an optimal level of 4 g of NaCl/1 was determined. In contrast, magnesium ion did not appear to affect growth or succinic acid production. A variety of complex nitrogen sources were also assessed, and a mixture of polypeptone, yeast extract, soytone, and peptone gave better results than any of these ingredients used alone (Lee et al. 1999). 

Since then, a considerable amount of structural and mechanistic information has been collected and yeast enolase is probably the best understood sequential enzyme to date. It is a homodimer and requires two Mg + ions per active site for catalytic activity under physiological conditions, although magnesium can be replaced with a variety of divalent metal ions in vitro. During a catalytic turnover, the metal ions bind to the active site in a kinetically ordered, sequential manner with differential binding affinities. The mode of action of yeast enolase is illustrated in Figure 26 and is unusually well understood since several solid-state structures for each intermediate identified with kinetic methods have been determined. 

Pyrophosphatases, which are present in all cells, and catalyze hydrolysis of inorganic pyrophosphate (PPj) to orthophosphate (P ) (see Chapter 6, Section D), also drive metabolic sequences. The very active pyrophosphatase of E. coli has a turnover number of over 2 x 104 s 1 at 37°C. The 1000 molecules per cell are sufficient to immediately hydrolyze any pyrophosphate produced by bacterial metabolism.733 The much studied soluble pyrophosphatases of E. coli,7 A 7 ,r yeast,736 and other organisms736ab are metalloenzymes that are most active with Mg2+. Two Mg2+ ions are held, mostly by carboxylate side chains, while a third apparently enters the active site as magnesium pyrophosphate, perhaps MgP20-. As with other metallohydrolases, a metal-bound hydroxyl ion may serve as the attacking nucleophile. 

Fio. 2. Proposed kinetic model for yeast inorganic pyrophosphatase. Here M represents Mg + but may also apply to any divalent cation with which the enzyme is active. In the rate equation A represents all mono-magnesium PPi complexes, B represents the di-magnesium complex, and I represents free PPi. Hydrogen ion equilibria are not considered. Kinetic runs were done at pH 7.4, 30° (9). Best values for kinetic constants were obtained from a computer program for nonlinear regression (9S). 

The requirement for minerals resembles that of other living cells and a supply of potassium, iron, calcium, magnesium, manganese, copper and zinc is necessary. Many of these metal ions and others are essential for the activity of enzymes. Relatively large amounts of phosphate and sulphate are also needed by brewing yeasts. 

Simple diffusion probably accounts for the uptake of undissociated organic acids by the yeast cell. Facilitated diffusion may be involved in the transport of sugars [17], although the fact that some are taken up against a concentration gradient could indicate that active transport occurs [18]. Active transport processes are used to transport amino acids and the ions of potassium, magnesium, phosphorus and sulphate. 

The strategy of wort supplementation with metal ions, lipids and yeast foods , with the aim to improve fermentation performance, is reviewed in detail by Gibson (2011). Among metal ions, zinc and magnesium were identified as elements with a crucial role in wort fermentation, the supplementation of which led to reduced attenuation time (Zn, Mg), increased uptake of trisaccharides (Zn) and increased ethanol production (Zn) and tolerance (Mg). It was also found that zinc has an indirect effect on the synthesis of higher alcohols and esters as well as on foam properties. Calcium supplementation of wort may only be beneficial when Ca concentration is limited in the local water supply (Gibson, 2011). 

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