And polypeptides

Short chains of amino acid residues are known as di-, tri-, tetrapeptide, and so on, but as the number of residues increases the general names oligopeptide and polypeptide are used. When the number of chains grow to hundreds, the name protein is used. There is no definite point at which the name polypeptide is dropped for protein. Twenty common amino acids appear regularly in peptides and proteins of all species. Each has a distinctive side chain (R in Figure 45.3) varying in size, charge, and chemical reactivity. 

The G-proteins are heterotrimers made of three families of subunits, a, P, and y, which can interact specifically with discrete regions on G-protein-coupled receptors. This includes most receptors for neurotransmitters and polypeptide hormones (see Neuroregulators). G-protein-coupled receptors also embrace the odorant receptor family and the rhodopsin-linked visual cascade. 

The amide linkage between monomer units in a protein is called a peptide bond. Peptides and polypeptides, which often exhibit biological activity (see Antibiotics, peptides Neuroregulators), are smaller than proteins. Although the differentiation between polypeptide and protein is somewhat arbitrary, the usual distinction is drawn around 100 monomer units. Proteins are also characterized by higher levels of stmcture resulting from internal interactions. 

With the exception of very large systems, e.g., polymer strands (Chapter 18) and polypeptides and polynucleotides (Chapter 16), all calculations have been carried out using ab initio Hartree-Fock theory with the 3-21G basis seF. The perfomance of this technique with regard to the calculation of geometries, relative energies, dipole moments and vibrational frequencies has been extensively documented. ... 

LC polyesters belong to the class of thermotropic main-chain LCPs, which also comprises polymers such as polycarbonates, polyethers, polyphenylenes, polyester-imides, polymers containing azo- or azo V-oxide linking groups, some cellulose derivatives, and polypeptides such as po 1 y (y - be n zy 1 -1. - g 1 u tamate). Both from the academic and industrial points of view, polyesters are by far the most important representatives of this class of polymers. 

Most oligopeptides and polypeptides do not give fluorescent adducts. (However, see Ref. 10.)... 

It can be concluded that MD is a very powerful tool to refine structures of proteins and polypeptides in solution, based on 2D NMR data. This combination of techniques emerges as an important means to determine the 3 D structure of macromolecules up to a molecular weight of 20,000 in solution or in micelles or membrane fragments. 

Self-Assembled Polypeptide and Polypeptide Hybrid Vesicles From Synthesis to Application... 

The preparation of polypeptide and polypeptide hybrid vesicles with predictable properties begins with proper synthesis of a primary structure. This section focuses on three different classes of procedures that are used to synthesize polypeptides. Although conjugation between the polypeptide and non-polypeptide blocks to form polypeptide hybrids is discussed briefly with the third class of synthesis procedures (Sect. 2.3), more detailed information regarding the synthesis and generation of polypeptide hybrid macromolecules are reviewed elsewhere [22-26]. 

Amphipilic polypeptides that are synthesized with appropriate ratios of hydrophilic to hydrophobic blocks can form ordered vesicular shapes. Although many polypeptides can self-assemble into vesicles when simply dissolved in the correct solvent, others require more processing steps. This section provides an overview of the techniques that have been developed to process various polypeptide and polypeptide hybrid systems into vesicles. 

Researchers studying polypeptide and polypeptide hybrid systems have also processed vesicles using two solvents. This method usually involves a common organic solvent that solubilizes both blocks and an aqueous solvent that solublizes only the hydrophilic block. The two solvents can be mixed with the polypeptide or polypeptide hybrid system at the same time or added sequentially. The choice of organic solvent depends heavily upon the properties of the polypeptide material, and commonly used solvents include dimethylformamide (DMF) [46, 59], methanol (MeOH) [49], dimethyl sulfoxide (DMSO) [50, 72], and tetrahydrofuran (THF) [44, 55]. Vesicles are usually formed when the organic solvent is slowly replaced with an aqueous solution via dialysis or removed through evaporation however, some vesicles have been reported to be present in the organic/aqueous mixture [49]. 

Many techniques used in other fields have been adapted to visualize and characterize vesicles composed of polypeptide and polypeptide hybrid systems. This section will describe these different approaches. 

Peptide-Based and Polypeptide-Based Hydrogels for Drug Delivery and Tissue Engineering... 

Hydrogels Based on [l-Sheet Structures of Peptides and Polypeptides. 146... 

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