Phenylalanine residues

However, the use of a HPLC separation step enabled a remarkable acceleration of the deconvolution process. Instead of preparing all of the sublibraries, the c(Arg-Lys-O-Pro-O-P-Ala) library was fractionated on a semipreparative HPLC column and three fractions as shown in Fig. 3-2 were collected and subjected to amino acid analysis. According to the analysis, the least hydrophobic fraction, which eluted first, did not contain peptides that included valine, methionine, isoleucine, leucine, tyrosine, and phenylalanine residues and also did not exhibit any separation ability for the tested racemic amino acid derivatives (Table 3-1). 

WEB A tripeptide contains valine, lysine, and phenylalanine residues. 

Only a few residues show more than 75% sequence identity, including four glycine residues, a proline residue at the beginning of the Pro loop, and a phenylalanine residue in a position corresponding to the conserved residue Tyr 165 of the bovine heart Rieske protein. However, structure prediction and sequence comparison with Rieske proteins from bci complexes suggests that the fold will be very similar in all Rieske-type ferredoxins, as in the other Rieske or Rieske-type proteins (see Section III,B,1). 

Schiller PW, Weltrowska G, Nguyen TM-D, Lemieux C, Chung NN, Marsden BJ, Wilkes BC. Conformational restriction of the phenylalanine residue in a cyclic opioid peptide analogue effects on receptor selectivity and stereospecificity. J Med Chem 1991 34 3125-3132. 

Sapse et al.41b performed ab initio calculations on benzene-benzene as a model for the interaction between the a phenylalanine residue and the benzoyl portion of a typical folate compound. In addition, that study examined the complex formed hy a benzene ring and a polar serine which acts as a hydrogen donor, between a benzene ring and the amino group of a meta diamino-imidazole group (present in some anti-folates) and between serine as a hydrogen donor and the diamino-imidazole group as the electron donor. 

Figure 1.19 Tyrosine and phenylalanine residues can undergo oxidation to modify their phenyl side-chain groups. Tyrosine can form covalent dimers that link two side chains together via a radical reaction. Both tyrosine and phenylalanine can be modified by oxidation to add oxygen-containing groups directly to their aromatic ring.

Several studies have been devoted to determine the localization of end-groups in modified polypropylene imine) dendrimers. Goddard et al. [ 157] and Cavallo and Fraternali [158] investigated the properties of the dendritic box, a fifth-generation polypropylene imine) dendrimer functionalized with (t-BOC)-pro-tected L-phenylalanine residues (Figure 16.12a) [159]. 

Selenoprotein A is remarkably heat stable, as seen by the loss of only 20% of activity on boiling at pH 8.0 for lOmin (Thrner and Stadtman 1973). Although selenoprotein A contains one tyrosine and no tryptophan residues, it contains six phenylalanine residues and thus has an unusual absorbance spectrum (Cone et al. 1977). Upon reduction, a unique absorption peak emerges at 238 nm, presumably due to the ionized selenol of selenocysteine, which is not present in the oxidized enzyme. The activity of selenoprotein A was initially measured as its ability to complement fractions B and C for production of acetate from glycine, in the presence of reducing equivalents (e.g., dithiothreitol). Numerous purification schemes were adopted for isolation of selenoprotein A, all of which employed the use of an anion exchange column to exploit the strongly acidic character of the protein. 

The actual information transfer is based on the interaction between the mRNA codons and another type of RNA, transfer RNA (tRNA see p. 82). tRNAs, of which there are numerous types, always provide the correct amino acid to the ribosome according to the sequence information in the mRNA. tRNAs are loaded with an amino acid residue at the 3 end. Approximately in the middle, they present the triplet that is complementary to each mRNA codon, known as the anticodon (GAA in the example shown). If the codon UUC appears on the mRNA, the anticodon binds a molecule of Phe-t-RNA to the mRNA (5) and thus brings the phenylalanine residue at the other end of the molecule into a position in which it can take over the growing polypeptide chain from the neighboring tRNA (6). 

Non-pyridoxal Phosphate Dependent. Figure 2 depicts the postulated mechanism for a non-pyridoxal phosphate catal) zed decarboxylation of histidine to histamine involving a pyruvoyl residue instead of pyridoxal -5 - phosphate (20). Histidine decarboxylases from Lactobacillus 30a and a Micrococcus sp. have been shown to contain a covalently bound pyruvoyl residue on the active site. The pyruvoyl group is covalently bound to the amino group of a phenylalanine residue on the enzyme, and is derived from a serine residue (21) of an inactive proenzyme (22). The pyruvoyl residue acts in a manner similar to pyridoxal phosphate in the decarboxylation reaction. 

A consequence of the existence of this equilibrium was the formation of a monosulfide (114) in the reaction of the simple dehydrocyclodipeptide (113) with an alanine or phenylalanine residue, as shown in Scheme 36. The reaction could have proceeded by replacement of the OMe by SH, followed by protonation of the exocyclic double bond and intramolecular attack by the thiol group. Alternatively, the m-dithiol could have been in equilibrium with the /rani-dithiol in the latter, a traw.v-annular attack could have generated the monosulfide. 

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