Hydrogen-deuterium exchange enzymes

If a carbanion is thermodynamically accessible, but is subject to rapid quenching by internal return of C02 in the case of decarboxylation, or by a proton in carboxylation, or in a hydrogen/deuterium exchange reaction, then the carbanionic intermediate off the enzyme would give the appearance of greater basicity than its thermodynamic value would predict. The localized character of the carbanion at the 6-position of UMP requires that the proton that is removed by a base in solution initially remains closely associated, and therefore, to a great extent be transferred to the carbanion. This reduces the rate of exchange and creates a discrepancy between kinetic and thermodynamic acidities. 

Contents J.A.Fee Copper Proteins - Systems Containing the Blue Copper Center. -M.F. Dunn Mechanisms of Zinc Ion Catalysis in Small Molecules and Enzymes. - W. Schneider Kinetics and Mechanism of Metalloporphyrin Formation. - M. Orchin, D. M. Bollinger Hydrogen-Deuterium Exchange in Aromatic Compounds. 

Coenzyme dissociation is rate limiting for both enzymes [341,4 3). Furthermore, no kinetic evidence has been obtained for an isomerization of the binary YADH-NADH complex, in contrast to the corresponding LADH complex 303). Hydrogen-deuterium exchange studies (464), however, indicate a conformational change upon coenzyme binding. 

The similarity between the hydrogen-deuterium exchange reaction of the aryldiimide- and arylhydrazine-platinum intermediates of this model and of N2ase is the best evidence for enzyme-bound diimide and hydrazine as intermediates (66). The correlation between the relative aflSnity of various ligands for N2ase and for some of the synthetic complexes of Fe, Co, Ni, Mo, Ru, Rh, Re, Os, and Ir that bind, but have not yet been shown to reduce, N2 (Table VIII) indicate that these metal complexes... 

Infrared spectroscopy has been used advantageously in studies of enzymatic reactions. Chapter 11 contains a discussion of the application of the infrared method of studying hydrogen-deuterium exchange in various enzyme molecules, and the application of this method for studying the effects of substrates and of inhibitor substances on the conformations of the enzymes. 

Rob, T, GiU, P.K., Golemi-Kotra, D., Wilson, D.J. (2013) An electrospray ms-coupled microfluidic device for sub-second hydrogen/deuterium exchange pulse-labeUing reveals allosteric effects in enzyme inhibition. Lab on a Chip, 13 (13), 2528-2532. 

Liu, Y.H., Konermann, L. (2006) Enzyme conformational dynamics during catalysis and in the resting state monitored by hydrogen/deuterium exchange mass spectrometry. FEBS Letters, 580 (22), 5137-5142. 

Akashi, S., Takio, K (2000) Characterization of the interface structure of enzyme-inhibitor complex by using hydrogen-deuterium exchange and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Protein Sci, 9 (12), 2497-2505. 

ESI Study of conformational dynamics of an enzyme, sub-second hydrogen/deuterium exchange Eiuni et al. [321]... 

This mechanistic proposal has extensive experimental support Imine 16 has been trapped and localized, and enzyme-catalyzed hydrogen/deuterium (H/D) exchange at C3 and C4 of DXP as well as carbonyl oxygen exchange has been detected. Acyl transfer to the C4 hydroxyl (18 to 19) as well as transfer of oxygen from DXP to nascent ThiS-COOH (21 to 22) has been demonstrated. Intermediate 22 has been trapped and detected by mass spectrometric analysis and the reaction product 14 has been fully characterized. Thiazole synthase complexed with ThiS-COOH has been structurally characterized and the DXP imine 16 has been modeled into the active site revealing key catalytic residues. ... 

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