Magnesium, as cofactor

Transfer of a two-carbon unit from a 2-keto sugar to the carbonyl carbon (Ci) of an aldose by a transketolase, which requires thiamine pyrophosphate and magnesium as cofactors. A covalent enzyme-substrate intermediate is formed similar to the one that occurs during the pyruvate dehydrogenase reaction (Chapter 13). 

Type II site-specific deoxyribonuclease [EC 3.1.21.4], also referred to as type II restriction enzyme, catalyzes the endonucleolytic cleavage of DNA to give specific, double-stranded fragments with terminal 5 -phosphates. Magnesium ions are required as cofactors. 

The project encompassed the comparative characterization of pyruvate decarboxylase from Z. mohilis (PDC) and benzoylformate decarboxylase from P. putida (BED) as well as their optimization for bioorganic synthesis. Both enzymes require thiamine diphosphate (ThDP) and magnesium ions as cofactors. Apart from the decarboxylation of 2-ketoacids, which is the main physiological reaction of these 2-ketoacid decarboxylases, both enzymes show a carboligase site reaction leading to chiral 2-hydroxy ketones (Scheme 2.2.3.1). A well-known example is... 

Some elements are essential to the composition or function of the body. Since the body is mostly water, hydrogen and oxygen are obviously essential elements. Carbon (C) is a component of all life molecules, including proteins, lipids, and carbohydrates. Nitrogen (N) is in all proteins. The other essential nonmetals are phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), fluorine (F), and iodine (I). The latter two are among the essential trace elements that are required in only small quantities, particularly as constituents of enzymes or as cofactors (nonprotein species essential for enzyme function). The metals present in macro amounts in the body are sodium (Na), potassium (K), and calcium (Ca). Essential trace elements are chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), molybdenum (Mo), nickel (Ni), and perhaps more elements that have not yet been established as essential. 

Pyruvate is initially decarboxylated into ethanal by pyruvate decarboxylase. This enzyme needs magnesium and thiamine pyrophosphate as cofactors (Hohmann 1996). Thereafter, alcohol dehydrogenase reduces ethanal to ethanol, recycling the NADH to NAD+. There are three isoenzymes of alcohol dehydrogenase in Saccharomyces cerevisiae, but isoenzyme I is chiefly responsible for converting ethanal into ethanol (Gancedo 1988). Alcohol dehydrogenase uses zinc as cofactor (Ciriacy 1996). 

The alkaline earths are chemically rather similar, and with the exception of beryllium and, to som6 extent, magnesium which have a pronounced tendency towards covalency, they form essentially ionic compounds. Both calcium and magnesium ions play a key role in various physiological processes by acting as cofactors in many enzymic reactions. In contrast beryllium is characterized by its extreme toxicity. (96)... 

A few basic components are needed to perform a PCR. First, two specific ofigonucle-otides (15-25 nt), called primers, are needed. They are derived from both strands of the target sequence, thus they determine the size and specificity of the resulting PCR product. The other components are a thermo-stable DNA polymerase, deoxyribonu-cleotides and a defined reaction buffer, which contains magnesium ions as cofactor and estimates the optimal reaction conditions for the polymerization of DNA (Saiki et al., 1988). 

All synthesis of amide bonds of biological significance are dependent upon energy, commonly in the form of ATP and of magnesium or manganese ions as cofactor. Some syntheses of amide bonds take place without the presence of any known coenzyme and others are dependent upon coenzyme A (CoA). The synthesis of acetyl sulfanilamide from acetate and sulfanilamide is an amide bond synthesis dependent upon CoA. This conjugation reaction has been studied by Chou and lipmann (1952) who showed that two enzymes took part in the reaction and that acetyl-l.S CoA was an intermediate product. 

HES is produced from 93—96% dextrose hydrolyzate that has been clarified, carbon-treated, ion-exchanged, and evaporated to 40—50% dry basis. Magnesium is added at a level of 0.5—5 mAf as a cofactor to maintain isomerase stabiUty and to prevent enzyme inhibition by trace amounts of residual calcium. The feed may also be deaerated or treated with sodium bisulfite at a level of 1—2-mAf SO2 to prevent oxidation of the enzyme and a resulting loss in activity. 

Magnesium is the second most abundant intracellular cation. Magnesium serves as an essential cofactor for numerous enzymes and in many biochemical reactions, including reactions involving adenosine triphosphate (ATP).17 Magnesium disorders can be multifactorial and can be related to renal function, disease... 

Some examples of cofactors are collected in Table 2 and include inorganic ions as iron(II), magnesium(II), calcium(II), zinc(II), etc compounds of high group transfer potential such as ATP and GPT involved in energy coupling with cells ... 

ATP and magnesium were required for the activation of acetate. Acetylations were inhibited by mercuric chloride suggesting an SH group was involved in the reaction either on the enzyme or, like lipoic acid, as a cofactor. Experiments from Lipmann s laboratory then demonstrated that a relatively heat-stable coenzyme was needed—a coenzyme for acetylation—coenzyme A (1945). The thiol-dependence appeared to be associated with the coenzyme. There was also a strong correlation between active coenzyme preparations and the presence in them of pantothenic acid—a widely distributed molecule which was a growth factor for some microorganisms and which, by 1942-1943, had been shown to be required for the oxidation of pyruvate. 

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