Methionine deuterated

Another important area of dynamic studies in biological samples is the effect of hydration upon molecular mobility in proteins and carbohydrates. The reason for these studies is primarily that protein dynamics, in particular, are crucial to their function, and so examining factors, such as the degree of hydration, that affect their dynamics is very important. However, it is obviously near-impossible to study dynamics in aqueous solution as a function of degree of hydration, and, since most proteins are not soluble in nonaqueous solvents, solid-state studies must be used. The motions at three methionine (Met) residues in Streptomyces subtilisin inhibitor (SSI) were studied with 2H NMR using a sample in which the Met residues at two crucial enzyme recognition sites (PI and P4) were specifically deuterated, along with one in the hydrophobic core.114 The motions of the Met side-chains were then examined... 

The identification of the radical in cytochromec peroxidase proved more elusive, partly because the EPR spectrum contains no well-resolved proton couplings. However, it was possible to identify this radical as being tryptophan-based by the effect of deuterated tryptophan on the couplings observed in the ENDOR spectra [27], No effect was observed when deuterated methionine was used. 

Fig. 8. EPR spectra of in cyanobateria (Met-27 mutant Anabaena variabilis) grown in a medium supplemented with 90 pM protonated methionine (A) 90 pM deuterated methionine (B) and wild-type Synechocystis-6802 cells grown in medium containing 0.5 mM phenylalanine, 0.25 mM tryptophan and 0.25 mM perdeuterated tyrosine (C). All spectra were recorded 2 min after illumination. The three signals were measured at a gain of 3.2, 3.2 and 5, respectively. Figure source Barry and Babcock (1987) Tyrosine radicals are involved in the photosynthetic oxygen-evolving system. Proc Nat Acad Sci, USA 84 7100.

The nsefnlness of this approach is demonstrated in identifying the secondary structure of methionine enkephalin (YGGFM) [46]. A controversy has persisted in the literature as to whether this peptide forms a 5 -> 2 P-tum or a 4 1 P-tum structure. By acquiring the CID-MS/MS spectrum of the deuterated peptide in a 50% trifluoroethanol-di/D20 solvent mixture, it was revealed that methionine enkephalin forms a 5 2 P-tum structure. 

The use of deuterated internal standards has been reported for the quantification of endogenous peptides, prostaglandins, pharmaceutical drugs, and the drugs of abuse. In the quantification of methionine enkephalin [1,5-7] and P-endorphin [1,5-7], the deuterium was incorporated in the phenyl ring of the phenylalaline and Ile residues, respectively. The phenyl ring-deuterated IS was also used in the quantification of p.-opioid receptor agonist Tyr-D-Arg-Phe-Lys-NH2 from ovine plasma [8],... 

Fig. 5. NMR spectrum at 100 MHz of staphylococcal nuclease in 0.3 M NaCl in D2O at pD 8.0 and 32 °C. (a) 20% solution of the protonated form after 60 scans, (b) 6% solution of the deuterated form after 129 scans histidine (S), tyrosine (Y), tryptophan T and methionine (S —CH3) (M) resonances are indicated. Shifts are measured with respect to hexamethyl-disiloxane as external standard. (From ref. 11, reproduced by permission)...

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