83181-79-7Relevant articles and documents
Methyl Side-Chain Dynamics in Proteins Using Selective Enrichment with a Single Isotopomer
Chaykovski, Michael M.,Bae, Lynnette C.,Cheng, Minn-Chang,Murray, Jenny H.,Tortolani, Kenneth E.,Zhang, Rui,Seshadri, Kothandaraman,Findlay, John H. B. C.,Hsieh, Shih-Yang,Kalverda, Arnout P.,Homans, Steve W.,Brown, Jonathan Miles
, p. 15767 - 15771 (2003)
13C relaxation studies on side-chain methyl groups in proteins typically involve measurements on 13CHD2 isotopomers, where the 13C relaxation mechanism is particularly straightforward in the presence of a single proton. While such isotopomers can be obtained in proteins overexpressed in bacteria by use of 13C enriched and fractionally deuterated media, invariably all possible 2H isotopomers are obtained. This results in a loss of both resolution and sensitivity, which becomes particularly severe for larger proteins. We describe an approach that overcomes this problem by chemical synthesis of amino acids containing a pure 13CHD2 isotopomer. We illustrate the benefits of this approach in 13C side-chain relaxation measurements on the mouse major urinary protein selectively enriched with [γ 1,γ2-13C2,α,β ,γ1,γ1,γ2,γ 2-2H6] valine. Relaxation measurements in the absence and presence of pyrazine-derived ligands suggest that valine side-chain dynamics do not contribute significantly to binding entropy.
The biosynthesis of branched dialkylpyrazines in myxobacteria
Nawrath, Thorben,Dickschat, Jeroen S.,Kunze, Brigitte,Schulz, Stefan
experimental part, p. 2129 - 2144 (2011/05/12)
The biosynthesis of the volatiles 2,5- and 2,6-diisopropylpyrazine (2 and 3, resp.) released by the myxobacteria Nannocystis exedens subsp. cinnabarina (Na c29) and Chondromyces crocatus (strains Cm c2 and Cm c5) was studied. Isotopically labeled precursors and proposed pathway intermediates were fed to agar plate cultures of the myxobacteria. Subsequently, the volatiles were collected by use of a closed loop stripping apparatus (CLSA), and incorporation into the pyrazines was followed by GC/MS analysis. [2H 8]Valine was smoothly incorporated into both pyrazines clearly establishing their origin from the amino acid pool. The cyclic dipeptide valine anhydride (16) - a potential intermediate on the biosynthetic pathway to branched dialkylpyrazines - was synthesized containing 2H1 labels in specific positions. Feeding of [2H16]-16 and [2H12]-16 in both valine subunits mainly resulted in the formation of pyrazines derived from only one labeled amino acid, whereas only traces of the expected pyrazines with two labeled subunits were found. To investigate the origin of nitrogen in the pyrazines, a feeding experiment with [15N]valine was performed, resulting in the incorporation of the 15N label. The results contradict a biosynthetic pathway via cyclic dipeptides, but rather point to a pathway on which valine is reduced to valine aldehyde. Its dimerization to 2,5-diisopropyldihydropyrazine 36 and subsequent oxidation results in 2. The proposed biosynthetic pathway neatly fits the results of earlier labeling studies and also explains the formation of the regioisomer 2,6-diisopropylpyrazine 3 by isomerization during the first condensation step of two molecules valine aldehyde. A general biosynthetic pathway to different classes of pyrazines is presented.
