The helical (commonly right-handed) form present in many proteins, deduced by Pauling and Corey from X-ray diffraction studies of proteins such as alpha-keratin; the helix is stabilised by hydrogen bonds between, e.g., ==C==O and HN== groups (symbolised by the centre dot in ==CO-HN==) of different eupeptide bonds. In a true a helix, there are 3.6 amino acid residues per turn of the helix.

Synonyms: 3.613 helix, Pauling-Corey helix.

Collagen helix, an extended left-handed helix resulting from the high levels of glycine, l-proline, and l-hydroxyproline present in the collagens. There are 3.3 amino acids per turn of the helix. Three of those left-handed helices form a triple superhelix that is right-handed.

(05 Mar 2000)

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