Introduction
Collagen is a protein that is most prevalent in mammals
and it is located almost all over the body, constituting
1/3 of the mass of all proteins. In the skin it amounts
to approximately 70% of the proteins’ mass [1]. A collagen
molecule, often called tropocollagen, consists of three subunits,
each of which turns left every three amino acid
residues. The three chains create a clockwise spiral,
which is called a triple helix structure [2]. The triple helix
is a tightly packed structure, through covalent and hydrogen
bonds formed by L-hydroxylysine and L-hydroxyproline.
In building the structure of this protein, depending on
the genetic type and origin, from 19 to 21 amino acids are
involved [3]. Construction of collagen is based on the structure
defined by the formula: (X-Y-Gly)n, in which every third
amino acid residue is glycine. Glycine (Gly) as a small amino
acid is able to fit in the center of the spiral, at the junction
of three chains. Other amino acids which are marked with
symbols X and Y in the formula, are usually Pro (L-proline)
or Hyp (4-L-hydroxyproline) and they constitute approxi