Manganese complexes ternary

The binding of Mg or Mn has been characterized by the use of ESR in the manganese case. This shows one tight-binding active site, four intermediate sites, and additional sites of low affinity that cause inhibition when occupied by Mn. Both tight and intermediate sites have to be occupied for activity in the case of Mg. A study of relaxation rates of phosphorus and hydrogen atoms in the bound dTTP substrate with Mn at the active site has allowed distance measurements to be made for both the binary Mn-dTTP complex and the ternary DNA polymerase-Mn-dTTP complex. This has allowed the structures shown in Figure 17 to be proposed. 

In a similar way, it seems difficult to explain how Cu is bound to the manganese oxides that are formed in the water column and would thus have to scavenge Cu from solution at these low [Cu2+] levels. Straightforward competition between complexation in solution and on surfaces may be too simplistic. The formation of ternary complexes of metal ions with surfaces and organic ligands is a possible binding mechanism. It was demonstrated in some model systems (39), but is poorly known for natural systems. 

The chemical shift of the phosphorus resonance of various nucleotides has been studied as a function of pH in the presence and absence of RNase A. The signal shifts upheld on protonation of the phosphate and the apparent pATa of the phosphate group in 2 -CMP complex with RNase is the same as the pATa of histidine-119 in this enzyme as determined by n.m.r. From n.m.r. relaxation rates for the ternary complex manganese(n)-phosphate-E. coli alkaline phosphatase, it has been concluded that an outer-sphere complex is formed which has a shorter lifetime than the enzyme turnover rate. The latter conclusion is consistent with the participation of the complex in the enzymic reaction. 

Sigel, H. and Naumartn, C. F., Ternary complexes in solution. XXIV. Metal ion bridging of stacked purine-indole adducts. The mixed-ligand complexes of adenosine 5 -triphosphate, tryptophan, and manganese(II), copper(II), or zinc(II), /. Am. Chem. Soc., 98(3], 730, 1976. 

In some kinases, such as nucleoside diphosphate kinase, " an intermediate step is the phosphoryl transfer to a group belonging to the enzyme, as happens in ATPase and as was discussed in detail for alkaline phosphatase (Section V.B). In other kinases the phosphoryl transfer occurs directly from the donor to the acceptor in a ternary complex of the enzyme with the two substrates.Often metal ions like magnesium or manganese are needed. These ions interact with the terminal oxygen of the ATP molecule, thus facilitating the nucleophilic attack by the acceptor. The metal ion is often associated with the enzyme. For mechanistic schemes, see the proposed mechanism of action of alkaline phosphatase, especially when a phosphoryl enzyme intermediate is involved. 

Peroxidase forms a number of complexes with hydrogen peroxide. The activation mechanism of substrate molecules in the active center of peroxidase involves the formation of a ternary complex heme-H20-donor of electrons. The role of the iron ion consists of transferring electrons from the donor to the hydrogen peroxide molecule. Peroxidase is endowed, moreover, with the oxidase function which increases in the presence of divalent manganese ions. 

The dioximato-manganese(II) catalyst (3) increases the auto-oxidation rate of epinephrine (a catecholamine derivative) in Na2C03-NaHC03 buffer at room temperature. The proposed mechanism presumes the binding of O2 to the Mn complex, followed by the formation of a ternary intermediate active catalyst-02-substrate complex which disproportionates in the rate-determining step to the product adrenochrome. ... 

Most arene complexes are hexahapto, and ternary complexes usually have 18 valence electrons. The most known and used ones for their applications in arene synthesis are the arene-metal-tricarbonyls (columns of chromium and manganese), in particular the arene-chromium-tricarbonyl and the arene-manganese-tricarbonyl cations... 

From e.s.r. studies on copper(n)-alkaline phosphatase it is concluded that the two metal ions at the active site have at least three equivalent nitrogen ligands, probably histidyl side-chains. A preliminary report on n.m.r. relaxation rates for the ternary complex of the manganese(n) enzyme with phosphate indicates that the activation energy Ea. for phosphate exchange is 8.0 kcal mol. In addition, the lifetime of this ternary complex is much... 

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