Directional specificity along peptide

Moreover, those workers have also studied a series of peptides with reversed order of the terminal amino acids, H-Tyr-(Pro)n Trp OH. They found that in this case, the slopes of In fcet versus number, n, of Pro residues in the bridge were somewhat different than for the former series, and they attributed this difference to directional specificity of LRET along the peptide backbone... 

Cellular protein biosynthesis involves the following steps. One strand of double-stranded DNA serves as a template strand for the synthesis of a complementary single-stranded messenger ribonucleic acid (mRNA) in a process called transcription. This mRNA in turn serves as a template to direct the synthesis of the protein in a process called translation. The codons of the mRNA are read sequentially by transfer RNA (tRNA) molecules, which bind specifically to the mRNA via triplets of nucleotides that are complementary to the particular codon, called an anticodon. Protein synthesis occurs on a ribosome, a complex consisting of more than 50 different proteins and several stmctural RNA molecules, which moves along the mRNA and mediates the binding of the tRNA molecules and the formation of the nascent peptide chain. The tRNA molecule carries an activated form of the specific amino acid to the ribosome where it is added to the end of the growing peptide chain. There is at least one tRNA for each amino acid. 

RNA directs biosynthesis of various peptides and proteins essential for any living organisms. Protein biosynthesis seems to be catalysed by mRNA rather than protein-based enzymes and occur on the ribosome. On the ribosome, the mRNA acts as a template to pass on the genetic information that it has transcribed from the DNA. The specific ribonucleotide sequence in mRNA forms an instruction or codon that determines the order in which different amino acid residues are to be joined. Each instruction or codon along the mRNA chain comprises a sequence of three ribonucleotides that is specific for a given amino acid. For example, the codon U-U-C on mRNA directs incorporation of the amino acid phenylalanine into the growing protein. 

As the terms internal and external refer to specific positions along a PPII helix oriented against the SH3 surface, it is clear that an inversion of the chain direction will result in the reorientation of the external and internal sites relative to the SH3 surface. If a peptide belongs to class I,... 

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