Glutamine metal complexes

The LFMM FF for the oxidized Cu(II) centers was designed around suitable homoleptic species, viz., [Cu(imidazole)4]2+, [Cu(SCH3)4]2-, [Cu(S(CH3)2)4]2+, and [Cu(0=CH2)4]2+ (37). These complexes represent models for Cu-histidine, Cu-cysteine, Cu-methionine, and Cu-glutamine O/peptide respectively. Only the first of these species is known experimentally. However, it is amply documented that DFT gives excellent structures for metal complexes (64,65) so we can access the remaining species computationally (Fig. 20). 

The PIX experiment has been extensively applied to problems of the type presented by glutamine synthetase, where the putative intermediates are too unstable to study directly and information on their presence and rates of formation is needed. For tests of kinetic competence this technique can be superior to more direct experiments, in which isolated or synthesized intermediates are mixed with enzymes in order to construct active complexes and the rates of reactions are measured. In such experiments the rates are rarely if ever found to be kinet-ically competent, since the putative intermediate must bind to an enzyme form that is never generated in a catalytic cycle, and the rate at which the intermediate complex is formed will be less than the overall rate. In the PIX experiment only the normal catalytic reaction is used to generate the desired complexes. The main drawback to the PIX experiment is that it depends on the torion rate in an intermediate such as MgADP. When the torsion rate is slow, e.g., owing to metal complexation, the experiment fails. 

Electron paramagnetic resonance (continued) cobalt-thermolysin complex, 28 334, 335 exchange reactions, 31 106-107 glutamine synthetase, 28 358-364 invisible oxygen species, 31 94-95 metalloenzymes, 28 324, 326 metal particle size distribution, 36 99-100, 104... 

As discussed earlier, the enzymic reaction catalyzed by glutamine synthetase requires the presence of divalent metal ions. Extensive work has been conducted on the binding of Mn2+ to the enzyme isolated from E. coli (82, 109-112). Three types of sites, each with different affinities for Mn2+, exist per dodecamer n, (12 sites, 1 per subunit) of high affinity, responsible for inducing a change from a relaxed metal ion free protein to a conformationally tightened catalytically active protein n2 (12 sites) of moderate affinity, involved in active site activation via a metal-ATP complex and n3 (48 sites) of low affinity unnecessary for catalysis, but perhaps involved in overall enzyme stability. The state of adenylylation and pH value alter the metal ion specificity and affinities. 

The first two steps in the biosynthesis of tryptophan in Salmonella typhimurium involve the enzyme complex anthranilate synthase-phosphoribosyltransferase, which is a tetramer having two subunits of each enzyme. The anthranilate synthase catalyzes reaction (7) and the phos-phoribosyltransferase catalyzes two reactions the N-terminal portion cleaves glutamine to glutamate giving NH3 for the anthranilate synthase, while the C-terminal portion catalyzes reaction (8).3,1,312 All these reactions require M2+ cations. Orotate phosphoribosyltransferase binds four Mn2+ ions in a cooperative fashion kinetic data have been interpreted in a scheme where both metal-free and metal-containing enzyme catalyze the reaction.313... 

The free Gd3+ formed in the metal ion-assisted dissociation of the Gd3+ chelate will react with some of the endogenous ligands with the formation of Gd3+ complexes (Gd3+-citrate, Gd3+-glutaminate, etc.). In principle, the endogenous... 

A study of the mixed complexes formed by metal interactions with asparagine and glutamine has shown that quite a large proportion of asparagine in blood may be co-ordinated to zinc(n) and iron(n) as well as copper(n).246... 

The complexation of the Group IIB metals by amino-acid and related derivatives continues to be a subject of interest stability constants reported include those for histidine and its derivatives, histamine, glycylhistamine, aspartic and glutamic acids, aspargine, glutamine, glycine, cysteine, and alanine. " ... 

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