Hydrogen-deuterium exchange amino acids

Goshe M.B., Anderson V.E. Hydroxyl radical-induced hydrogen/ deuterium exchange in amino acid carbon-... 

Kinetics and stereochemistry of deuterium exchange of the a-hydrogen of an amino acid moiety in metal complexes of amino acid Schiff bases with or/Jio-hydroxy-acetophenone have been studied by Belokon et al.249). 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

It should be noted that many polar substances with poor solubilities in the usual solvents can be dissolved in water or in D2O. Examples of the potential use of aqueous solutions in pharmaceutical research are to be found in the discussions of aqueous solutions (thap. 3), enzymology (Chap. 15), hydrogen-deuterium exchange (Chap. 11), nucleic acids (Chap. 12), carbohydrates (Chap. 6), amino acids (Chap. 9), amines (Chap. 8), clinical chemistry (Chap. 18), and inorganic ions (Chap. 19). 

These co-ordinated amino acids are, thus, activated to electrophilic attack at the -position. One of the simplest manifestations is seen in the exchange of the methylene hydrogen atom for deuterium or tritium (Fig. 5-16). 

For two transaminases the remaining unknown stereochemical parameter was determined by demonstrating an internal transfer of tritium (dialkyl amino acid transaminase) [28] or deuterium (pyridoxamine-pyruvate transaminase) [27] from the a-position of the substrate L-alanine to C-4 of the cofactor. Internal hydrogen transfer from the a-position of the substrate amino acid to C-4 of PLP has also been demonstrated for two of the abortive transamination reactions, those catalyzed by tryptophan synthase fi2 protein [32] and by aspartate-/8-decarboxylase [31]. In addition, the same phenomenon must occur in alanine transaminase, as deduced from the observation that the enzyme catalyzes exchange of the /8-hydrogens of... 

As alluded to above, the studies of Aberhart and co-workers were further complicated by their observation that the total deuterium content in the products was always less than stoichiometric with the reactant amino acid. Since exchange with the solvent has been ruled out. Moss and Frey approached this problem by investigating the role of SAM in the aminomutase reaction (227). Their results suggest that the elusive hydrogen acceptor is SAM. Incubation of L-lysine with S-[2,8,5 - H]adenosylmethionine catalyzes the interconversion of L-lysine and )8-lysine with incorporation of tritium into both isomers. Essentially no tritium is observed in the products of the reaction when S-[2,8- H]adenosylmethionine or 5-adenosyl[mef/i> /- H]methionine is utilized. Furthermore, the distribution of... 

Determination of partial amino acid composition of peptides This can be accomplished by the identification of immonium ions (H2N=CHR" ) from the MS-MS spectra (Table 5.3). Alternatively, an exchange experiment with deuterium may increase 0 to 5m.u. per residue for the exchangeable hydrogens in a peptide. The total increase in peptide mass therefore reflects the peptide composition. 

The rate of the reversible 1,2-enolization can also be readily measured by NMR monitoring the exchange of methylene hydrogen atoms at C-1 with deuterium atoms from solvent D20. Within a series of D-fiuctose-amino acids, the enolization rates were affected by the stracture of Amadori compounds, flie temperature, and tire presence of phosphate nucleophihc catalyst (Table fV)-... 

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