Poly serine

FIGURE 2 Polymers that can be derived firom L-serine. (a) Poly-(serine ester) was obtained by ring opening polymerization of N-protected serine-p-lactones (19). (b) Poly(serine imine) has appar-... 

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. 

Alternatively, amino acids can be polymerized by linkages other than the conventional peptide bond, yielding pseudopoly(amino acids) [26]. For example, the amino acid serine can be used to produce poly(serine ester), poly(serine imine), or conventional polyserine ... 

In an effort to adjust the interface properties of polylactide (PLA) nanoparticles used for drug delivery, copolymers were synthesized having a polypeptide block in between PEG and PLA. One copolymer was prepared by polymerization of O-protected l serine-NCA with an amino-terminated PEG. Subsequently, the deprotected serine groups were used to polymerize lactide to produce a comb-like copolymer block. This copolymer was compared with a triblock copolymer PEG-h-poly(alanine)-h-PLA. In this case, the endgroup of the poly(alanine) block was used as initiator [54]. Both types of copolymers form nanoparticles, but the copolymers with the comb-like structure show particularly interesting properties. Zeta-potential measurements indicate that the poly (serine) backbone covers the PLA core. 

Thiostrepton family members are biosynthesized by extensive modification of simple peptides. Thus, from amino acid iacorporation studies, the somewhat smaller (mol wt 1200) nosiheptide, which contains five thiazole rings, a trisubstituted iadole, and a trisubstituted pyridine, is speculated to arise from a simple dodecapeptide. This work shows that the thiazole moieties arise from the condensation of serine with cysteiae (159,160). Only a few reports on the biosynthesis of the thiostrepton family are available (159,160). Thiostrepton is presently used ia the United States only as a poly antimicrobial vetetinary ointment (Panalog, Squibb), but thiazole antibiotics have, ia the past, been used as feed additives ia various parts of the world. General (158) and mechanism of action (152) reviews on thiostrepton are available. 

Zhou, Q. X., and Kohn, J., Preparation of poly(L-serine ester) A structural analog of conventional poly-L-serine, Macromole-cules. In Press. 

Scheme 18 Synthesis of water-soluble EG-grafted poly(L -serine)s...

Test results for a series of reactions of polyfunctional amino acids with CDI in aqueous solution are reported in reference [51]. Serine and threonine did not poly-condense. Instead, via the iV-imidazolyl-carbonyl amino acids, L-2-oxooxazolidine-4-carboxylic acid or L-(+)-fraw,s-5-methyl-2-oxooxazolidine-4-carboxylic acid were obtained. 

Most poly(HA) depolymerases are inhibited by reducing agents, e.g., dithio-erythritol (DTT), which indicates the presence of essential disulfide bonds, and by serine hydrolase inhibitors such as diisopropyl-fluoryl phosphate (DFP) or acylsulfonyl derivates. The latter compounds covalently bind to the active site serine of serine hydrolases and irreversibly inhibit enzyme activity [48]. 

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

Malcolm (1973, 1975) reported possible observable differences between the pressure-area curves of poly(L-alanine) mixed with poly(D-a-amino-n-butyric acid) and the corresponding mixture containing poly(D-alanine). Shafer (1974) observed differences in the film pressure between (/ )-phosphatidyl serine with poly-L-lysine and the corresponding film with poly-D-lysine injected under the film. 

Ohtake K, Maeno T, Ueda H, Ogihara M, Natsume H, Morimoto Y (2003) Poly-L-arginine enhances paracellular permeability via serine/threonine phosphorylation of ZO-1 and tyrosine dephosphorylation of occludin in rabbit nasal epithelium. Pharm Res 20 1838-1845. 

A high proportion of the positiveiy charged basic amino acids lysine and arginine within these flexible tails are frequent targets for extensive posttranslational modifications (Berger, 2002). Such modifications include the acetylation of lysine residues, the methylation of lysine and arginine residues, the ubiquitination of lysine residues, the phosphorylation of serine and threonine residues, the sumoylation of lysine residues, and the poly ADP-ribosylation of glutamic acid residues. 

Polyuridylic acid is a polynucleotide which can be used as a synthetic template RNA in a polypeptide synthesizing system (see Glossary for a discussion of these systems). It directs the incorporation of phenylalanine, and the product with poly U as template is polyphenylalanine. It has been observed that prior irradiation of the poly U template reduces its activity as a template.79,80 The amount of phenylalanine incorporation decreases with increasing dose of ultraviolet light, and some serine begins to become incorporated in the polypeptide chain. 

N 047 "Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. V. Serine Parameters from Random Poly(hydroxybutylglutamine-co-l-serine)"... 

Water-soluble random copolymers containing L-serine and A/5-(4-hydroxybutyl)-L-glutamine are prepared, and the thermally induced helix-coil transition of these copolymers in water is studied. The Z/mm-Bragg parameters cr and s for the (hypothetical) helix-coil transition in poly(l-serine) in water are deduced. The values of s, computed from both the Lifson and Allegra theories are (.Llfson, o-1 x 10-4 / Allegra, o = 7.5 x 10 5 s - 0.667/0.726 (273 K), 0.757/0.784 (293 K), 0.777/0.792 (313 K), 0.731/0.744 (333 K),... 

---