Magnesium ions group transfer

The formation of Grignard reagents takes place at the metal surface. Reaction commences with an electron transfer to the halide and decomposition of the radical ion, followed by rapid combination of the organic group with a magnesium ion.1 It... 

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 ... 

DNA polymerases catalyze DNA synthesis in a template-directed manner (Box 16). For most known DNA polymerases a short DNA strand hybridized to the template strand is required to serve as a primer for initiation of DNA synthesis. Nascent DNA synthesis is promoted by DNA polymerases by catalysis of nucleophilic attack of the 3 -hydroxyl group of the 3 -terminal nucleotide of the primer strand on the a-phosphate of an incoming nucleoside triphosphate (dNTP), leading to substitution of pyrophosphate. This phosphoryl transfer step is promoted by two magnesium ions that stabilize a pentacoordinated transition state by complex-ation of the phosphate groups and essential carboxylate moieties in the active site (Figure 4.1.1) [2],... 

The Grignard reagent is a classical organometallic compound. The magnesium ion in Group IIA of the periodic table needs to lose two and only two electrons to achieve the inert gas configuration. This metal h ts a strong tendency to form ionic bonds by electron transfer ... 

Here the side-chain is unrestricted but the required magnesium ion is thought to bind to both the carbonyl group to be reduced and the ring nitrogen center to bring the hydride-transfer distance into a range for reaction to occur. 

S-methyl group to one of the two hydroxyl groups of a catechol to give a methylated catechol and 5-adenosyl-L-homocysteine, Figure 8. Catechol 0-methyltransferase is a monomeric enzyme that catalyzes the O-methylation of a variety of catecholamine neurotransmitters such as dopamine. It requires magnesium ions [42], and the rate-determining step appears to be transfer of the methyl group [43, 44],... 

The catalytic center of RNAP includes the binding site for the 3 -end of RNA and the insertion site for the incoming rNTP. In the nucleotidyl transfer reaction, the 3 -OH group in the sugar ring of the RNA primer reacts with the a-phosphorous atom of a ribonucleoside triphosphate by nucleophilic attack, then the Pa-Oap bond is broken and pyrophosphate (PPj) is released. Thus, a nucleotidyl addition to the RNA primer is achieved. Structural and biochemical data have shown that the active centers of all polymerases share certain common features a pair of metal ions (normally divalent magnesium ions Mg " and three universally conserved carboxylates. The two-metal-ion mechanism for the nucleotidyl transfer reaction... 

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