Peptides alpha-helix polypeptides

Alpha helix. A helical conformation of a polypeptide chain, predominantly right-handed, with maximal intrachain hydrogen bonding of the peptide bonds one of the most common secondary structures in proteins. 

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... 

The alpha helix and the pleated sheets were discovered not by direct deduction from experimental observations on proteins but rather by theoretical considerations based on the study of simpler substances. In amino acids one carbon atom, called the alpha carbon atom, C , lies between the amino group and the carboxyl group. When amino acids combine with one another to form a peptide or polypeptide, with elimination of water, the atoms between two alpha carbon atoms have the following structure ... 

The wavelengths of IR absorption bands are characteristic of specific types of chemical bonds. In the past infrared had little application in protein analysis due to instrumentation and interpretation limitations. The development of Fourier transform infrared spectroscopy (FUR) makes it possible to characterize proteins using IR techniques (Surewicz et al. 1993). Several IR absorption regions are important for protein analysis. The amide I groups in proteins have a vibration absorption frequency of 1630-1670 cm. Secondary structures of proteins such as alpha(a)-helix and beta(P)-sheet have amide absorptions of 1645-1660 cm-1 and 1665-1680 cm, respectively. Random coil has absorptions in the range of 1660-1670 cm These characterization criteria come from studies of model polypeptides with known secondary structures. Thus, FTIR is useful in conformational analysis of peptides and proteins (Arrondo et al. 1993). 

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