Polyproline Poly

In the absence of an AGAC the ribosomes will prodnce the artificial polypeptides, polyphenylalanine (as specified by the codon UUU) or polyproline (as specified by the codon CCC). However, when streptomycin is added, the ribosomes prodnce a mixture of polythreonine (codon ACU) and poly serine (codon UCU). The misreading of the codons does not appear to be random U is read as A or C and C is read as A or U. If such misreading occurs in whole cells the accumulation of non-functional or toxic proteins would eventually prove fatal to the cells. There is some evidence that the bacterial cell membrane is damaged when the cells attempt to excrete the faulty proteins. 

A wave of excitement was set in motion by this discovery. Soon afterwards it was demonstrated that poly (A) promotes poly lysine synthesis and poly(C) promotes polyproline synthesis. From these observations it seemed clear that the code words UUU, AAA, and CCC correspond to the amino acids phenylalanine, lysine, and proline, respectively. 

Despite different sequences and repetitive motives, all gliadins have the same secondary structure of loose spirals which are a balanced compromise between the p-spiral and poly-L-proline structure (polyproline helix II) (Parrot et al., 2002), the balance is dependent on temperature, type of solvent, and hydration level (Miles et al., 1991). Similar sequences can be found in other proteins, mainly animal proteins such as elastin and collagen, and they are responsible for particular biomechanical properties connected to reverse P-spirals or p-sheet structures (Tatham and Shewry, 2000). 

In addition to the order-disorder transition, observed for a helices, helical structures can also be induced to undergo transitions from one ordered form to another. For example, a crystalline form of poly[p-(p-chlorobenzyl)-L-aspartate] can be made to undergo a phase transition from an a-helical to an co-helical form by heating rotational entropy is computed to play a role in this process.68 Another order-order transition is the solvent-induced interconversion between polyproline 1 (with cis peptide bonds) and polyproline 11 (with trans peptide bonds), a process that has also been subjected to conformational energy calculations.85 The transition has been accounted for in terms of differences in the binding of solvent components to the peptide 0=0 groups. 

The collagen triple helix has a unique CD spectmm. The spectrum shows a positive peak at 220-225 nm, and a negative peak at 195-200 nm. In contrast, the polyproline II helix has a positive peak at 228 nm, and a negative peak at 206 nm. The polyproline II like poly-4-hydroxyproIine helix has a positive peak at 219 nm and a negative peak at 205 nm (13). The thermal stability of the triple helix can be monitored easily by the CD... 

Similar experiments were carried out with different synthetic polyribonucleotides. It was found, for example, that polyadenylic acid (poly A) leads to the synthesis of polylysine, and that polycytidylic acid (poly C) leads to the synthesis of polyproline. By 1964, all 64 codons had been deciphered (Table 20.4). Nirenberg, R. W. Holley, and H. G. Khorana shared the 1968 Nobel Prize in Physiology or Medicine for their seminal work. 

In 1959, C. G. Overberger initiated a program to study various parameters which influenced the ordered conformation of polyproline type pol)nners the results demonstrate that substitution of a methyl group at the 2-posltion, poly-2-methylproline (P2MP), can perturb the conformation of the polymeric chains so that the resultant poljnner no longer behaves like a typical poly-L-proline system. However, substitution of a methyl group at the 5-position (cis- and trans-) resulted in only a small modification of... 

In contrast, polar media encourages the formation of the all-trans poly(L-pro-line)-n structure, which is an extended left-handed helix having a repeat length of three amino acids and a translation length of 3.12 A per residue. It should be noted that both polyproline structures exist as solvent-stabilized conformations which, unlike the a helix, do not rely on the formation of long-range, interresidue hydrogen bonds for their stability. Thus proline trimers [43] and tetramers [44] crystallized from aqueous solution have been shown to adopt the conformational... 

Mikhonin, A.V., Myshakina, N.S., Bykov, S.V., Asher, S.A. UV resonance Raman determination of polyproline II, extended 2.5i-heUx, and b-sheet y angle energy landscape in poly-L-lysine and poly-L-glutamic acid. J. Am. Chem. Soc. 127, 7712-7720 (2005)... 

Poly(L-proline) Polyproline prolinc homopolymer 25191-13-3 L-Proline, homopolymer R CC5H9N02)r... 

Fully extended chain p parallel structure p antiparallel structure Polyproline I (oj = 0") Poly proline II (w = ISO ) Polyglycine II Collagen... 

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