Linkage polypeptide

Formation ofdehydrohydroxylysinonorleucine linkage. Polypeptide chains (nonheBcal regions) ... 

Fibrous proteins Globular proteins Alpha-amino acids Side chains Dipeptide Peptide linkage Polypeptide Primary structure Secondary structure Alpha-helix Pleated sheet Tertiary structure Disulfide linkage Denaturation Enzymes... 

N-terminal Peptide linkage Polypeptide Primary structure Protein... 

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. 

The peptide linkage is usually portrayed by a single bond between the carbonyl carbon and the amide nitrogen (Figure 5.3a). Therefore, in principle, rotation may occur about any covalent bond in the polypeptide backbone because all three kinds of bonds (N——C, and the —N peptide bond) are sin-... 

Intrachain S—S (disulfide) cross-bridges between cysteine residues in the polypeptide chain are cleaved. (If these disulfides are interchain linkages, then step 2 precedes step 1.)... 

A variety of cellular and viral proteins contain fatty acids covalently bound via ester linkages to the side chains of cysteine and sometimes to serine or threonine residues within a polypeptide chain (Figure 9.18). This type of fatty acyl chain linkage has a broader fatty acid specificity than A myristoylation. Myristate, palmitate, stearate, and oleate can all be esterified in this way, with the Cjg and Cjg chain lengths being most commonly found. Proteins anchored to membranes via fatty acyl thioesters include G-protein-coupled receptors, the surface glycoproteins of several viruses, and the transferrin receptor protein. 

Using the same method a block copolymer of polypeptides and vinyl monomers was also prepared. As mentioned in Section II, Bamford and Mullik [22] introduced an interesting method of photoinitiation of vinyl monomers by the Mn2(CO)io or the Re2(CO)io/C2F4 system. By these methods polymeric molecule with (CO)sMn—CF2CF2—terminals is produced (see Scheme [12]). If a polymer of this kind is heated to 100°C in the presence of vinyl monomer, a block copolymer AB or ABA with Cp2- F2 linkage is produced [ ] ... 

A substantial number of bioactive molecules, such as polypeptides, N-acetyl-DL-penicillamine, p-(dipropylsulfamoyl)benzoic acid, and nicotinic acid, contain a carboxylic acid function, and this provides a site for linkage to a polyphosphazene chain. A number of prototype polymers have been synthesized in which pendent amino groups provide coupling sites for the carboxylic acid (34). The amide linkages so formed are potentially bioerodible, but the use of a hydrolytic sensitizing cosubstituent would be expected to accelerate the process. 

Based on the nature of the linkage between their polypeptide chains and their oligosaccharide chains, glycoproteins can be divided into three major classes (Figure 47-1) (1) those containing an O-glycosidic linkage (ie,... 

Fig. 2.—Schematic Representation of the Heparin Proteoglycan. [The polysaccharide chains, bound to the polypeptide matrix through a linkage region," are cleaved by tissue endoglycosidases (arrows) after the transformations illustrated in Scheme 1.]...

Kossjakow114 claims to have isolated a polysaccharide in this way, by a relatively simple procedure, but the reviewer and coworkers11 have been unable to obtain active material by this method. It does appear that the specific substances contain carbohydrate, lipid, and possibly polypeptide constituents similar perhaps to the Foreman antigen (see below) and that the linkages between these constituents are very fragile. 

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