Configuration, amino acid

Substitution of the l-amino acids with their D-amino acid configurational analogue, will enhance resistance to enzymatic cleavage of peptide bonds. The ll isomer of cyclo(Leu-Leu) hydrolyzes 3.5 times faster than the DL isomer in the presence of 0.5 moll HCl. This difference was explained by both steric shielding ui-trans isomer) and steric strain (ll- j isomer). ... 

Scheme 5 Synthesis of a t )[CH2-S] Pseudopeptide with the Natural l-l-Amino Acid Configuration Assuming the Stereochemical Transformations as Indicated 36 ...

Several studies have suggested the importance of the (3S) stereoconfiguration of the C-3 carbon atom on the enzyme interactions, which is equivalent to the natural L-amino acids configuration. The different substitution at the C-4 position has shown significant effect on the inhibitory power substituents such as... 

From the isolation of the O-deacylated but otherwise unmodified GPL from serovar 12, it was also shown that the structure of the lipopeptide core was identical to that accepted for glycolipids of this group with respect to D-amino acid configurations, but not of the alaninol unit, and of the mono-unsaturated monohydroxy fatty acid.48... 

Another program suite for finding templates and particular motifs in a huge preprocessed database containing common amino acid configurations was reported by Oldfield [86],... 

Two fragments were isolated by hydrolysis of the penicillins with acid. The first, penicillamine (3.2), was identified as p,p-dimethylcysteine by synthesis and shown to possess the unusual o-amino acid configuration. The second fragment, which retained the side-chain, was known as a penaldic acid (3.4). It behaved as a p-keto acid and lost carbon dioxide to give a penilloaldehyde... 

In act, we cannot use the right-handed acids in our bodies if they were the only type available to us, we could not survive. We do not know, however, why our amino acids are left-handed, nor what amino acid configurations (if any) may exist in extraterrestrial organisms. 

Of the standard a-amino acids, all but glycine can exist in either of two optical isomers, called L or D amino acids, which are mirror images of each other. While L-amino acids represent all of the amino acids found in proteins during translation in the ribosome, D-amino acids are found in some proteins produced by enzyme posttranslational modifications after translation and translocation to the endoplasmic reticulum, as in exotic sea-dwelling organisms such as cone snails. They are also abundant components of the peptidoglycan cell walls of bacteria, and D-serine may act as a neurotransmitter in the brain. The L and D convention for amino acid configuration refers not to the optical... 

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