Amino-acid-type-selective

Fig. 4.4 Example of amino acid-type selective labeling. A [ H,15N]-HSQC spectrum obtained with the fully 15N-labeled monomeric form of the KSHV protease. B and C [nH,15N]-l-ISQC spectra...

Instead of using amino acid-type selective labeling suppression of high background signals can also be achieved by selective expression of the protein of interest with the concomitant suppression of the expression of all other (host-) proteins. In principle, this suppression of host gene expres-... 

Mink M, Mosier SM, Janumpalli S, Davison D, Jin L, Melby T, Sista P, Erickson J, Lambert D, Stanfleld-Oakley SA, Salgo M, Cammack N, Matthews T, Greenberg ML (2005) Impact of human immunodeficiency virus type 1 gp41 amino acid substitutions selected during enfuvirtide treatment on gp41 binding and antiviral potency of enfuvirtide in vitro. J Virol 79 12447-12454... 

An affinity label is a molecule that contains a functionality that is chemically reactive and will therefore form a covalent bond with other molecules containing a complementary functionality. Generally, affinity labels contain electrophilic functionalities that form covalent bonds with protein nucleophiles, leading to protein alkylation or protein acylation. In some cases affinity labels interact selectively with specific amino acid side chains, and this feature of the molecule can make them useful reagents for defining the importance of certain amino acid types in enzyme function. For example, iodoacetate and A-ethyl maleimide are two compounds that selectively modify the sulfur atom of cysteine side chains. These compounds can therefore be used to test the functional importance of cysteine residues for an enzyme s activity. This topic is covered in more detail below in Section 8.4. 

Only those values of and ip which lie within the allowed regions of the steric map for each amino acid residue (of the type shown in Fig. 11) were used in the computation. Several allowed areas for each amino acid were selected at random, the number of such points being approximately proportional to the allowed area for each amino acid. Having selected a discrete set of amino acid, and regarding the atoms as hard spheres, all sterically-allowed conformations... 

Another way of overcoming spectral overlap for proteins is selective isotope labeling of one or several amino acid types, which results in less-crowded H- N spectra with cross-peaks from the labeled residues only. The same is possible for RNA where nucleotides can be selectively isotope enriched. In addition, methods for segmental labeling of parts of the biomolecules have been developed for proteins (48, 49) and for RNA (50). 

Transfer RNA (tRNA) Is the key to deciphering the codons in mRNA. Each type of amino acid has Its own subset of tRNAs, which bind the amino acid and carry It to the growing end of a polypeptide chain If the next codon in the mRNA calls for It. The correct tRNA with Its attached amino acid is selected at each step because each specific tRNA molecule contains a three-nucleotide sequence, an anticodon, that can base-pair with Its complementaiy codon in the mRNA. 

Dehydrated milk-based foods is the major source of D-lactulose-amino acids in human nutrition. The dairy industry widely uses milk dehydration to manufacture powdered milk as a base for numerous dairy products, such as infant formulas, confectionaries, reconstituted milk etc. During the process of heating, drying and storage, lactose in milk can readily interact with amino compounds that are naturally present, primarily lysine residues in milk proteins. Estimated contents of D-lactulose-amino acids in selected products are compiled in Table 2. Commercial dairy products may contain, therefore, up to 40% of protein lysine in form of lactulose-lysine. Dietary availability of D-lactulose-amino acids is similar to that of the fructosamine derivatives. An ample evidence exists that the Amadori-type lysine glycoconjugates are not available to mammals as a nutrient and that lactulose-lysine is partially absorbed into the bloodstream and excreted unchanged. ... 

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