Phenylalanine residues replacement

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. 

Biphalin, in standard receptor-binding assays, shows twice the affinity to mu than delta receptors (Table 1). Structure-activity relationships of a series of symmetric biphalin analogues show that replacing phenylalanine residues with -chlorophenylalanine increases the affinity for delta receptors and decreases it for mu receptors, resulting in more potent and more... 

Aval, Aile, Aala, Anva, Aleu, Anle, and Aphe are valine, isoleucine, alanine, norvaline, leucine, norleucine, and phenylalanine residues where the a-CH has been replaced by a nitrogen atom. 

On the left is a section of normal protein with glycine and phenylalanine residues (Chapter 49). In the middle is the intermediate formed when a molecule of water attacks the amide carbonyl group. On the right is a piece of the HIV protease inhibitor. The amide nitrogen atom has been replaced by a CH2 group (ringed in black) so that no hydrolysis of the C-C bond can occur. The inhibitor may bind but it cannot react. 

Tetanus toxin (TeTx) is a zinc-dependent protease that has been shown to cleave VAMP-1, VAMP-2 and cellubrevin (Niemann ef al., 1994). The toxin usually cleaves between a glutamine and a phenylalanine residue. The cleavage site of rat VAMP-1 is slightly different as the glutamine residue is replaced by valine. For this reason rat VAMP-1 is a poor substrate for TeTx (Niemann et al., 1994). Since the toxin is highly specific for VAMPs, it is a powerful tool to investigate the role of these proteins in different cellular processes. 

The N-terminus of riboflavin synthases from eubacteria, fungi, and plants is marked by an extraordinary degree of sequence conservation. The canonical amino acid sequence is MFTG, and no N-terminal extensions beyond that motif are known. The replacement of the phenylalanine residue by any amino acid except tyrosine nullifies the catalytic activity of the protein. ... 

Antibiotics closely related to pristinamycin Ia include virginiamycin Sj (6), where the iV-methyl 4-dimethylamino phenylalanine residue is replaced by iV-methyl phenylalanine and vernamycin C (7,=doricin), where the 4-oxo-pipecolic acid residue is replaced by aspartic acid. 

By serial replacement, it was found that the three active parts of the enkephalins are the —OH and —NH of the tyrosine fragment, and the lipophilic area in the phenylalanine residue (successfully replaceable by other lipophilic groups) (Gorin et al., 1980). Swiss workers who made stepwise changes to the molecule of Af enkephalin, produced FK 33-824 which is 1000 times as potent as morphine by intra-cerebroventricular injection in laboratory animals (Roemer et al., 1977), but has anaphylactoid side effects in Man. A French group then discovered thiorphan, an (artificial) dipeptide that... 

In particular, the reduction of NMeN approximates the replacement of several valine residues by phenylalanine residues. Just as... 

Effect of Different Pentamer Sequence Arrangements of the Same 30-mer Composition. Chemically synthesized polytricosapeptides, poly (30-mers), were prepared with compositions of 1 aspartic acid residue (Asp, D) and 5 more-hydrophobic phenylalanine (Phe, F) residues replacing valine (Val, V) residues per repeat of 30 residues, but with different relative locations of D and F residues. These compositions are written ... 

Tyrosine or phenylalanine residues in position 2 are essential for activity. Replacement of the aromatic amino acid by serine inactivates the hormone completely. The phenylalanine derivative is less active than the tyrosine derivative, indicating that the hydroxyl group of tyrosine, although not essential, enhances the hormonal activity. 

C random coil turns into a P-spiral and precipitate Tcp is dependent on pH and the ionic strength Hydrophobidty and conformational preferences of the constituent amino acids define the LOST behaviour Top of the peptides could be adjusted by replacing valine residues by more hydrophobic isoleudne, leudne or phenylalanine residues [329]... 

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