Conservation Science

96 Chapter 5

skin’s leather-making fibres, the nature of their putrefaction and the proper-
ties of the wide variety of materials, which are employed to prevent this.

2.2 Collagen

It has been shown that the fibres and fibre bundles which make up most of the
skin structure, and which are retained and stabilised during the pretanning
and tanning processes, consist mainly of the protein collagen. All proteins are
formed from amino acid residues linked together. The properties of any par-
ticular protein are determined by which residues are present, and the order
and configuration in which they are joined. The collagen in skin exists as long,
unbranched, macromolecular chains, each formed from just over 1000 amino
acid residues. About 30% of these residues are derived from the smallest
amino acid, glycine. A further 10% each are from the five-membered, ring-
structured imino acids proline and hydroxyproline. Also present are signifi-
cant quantities of acidic residues from aspartic and glutamic acids and basic
residues derived from, for example, arginine and lysine (Figure 1).

O

H

H N

H

glycine

O

H

H N

H

H

O

OH

aspartic acid

O

H

H N H

H H

H

O

OH

glutamic acid

N

H

H

H

H

H

O

H

H

proline

N

H

H

H

H

OH

O

H

H

hydroxyproline

N

H

H

O

H

H N H

H H

H

H

H

H

H

lysine

O

H

H N H

H H

H

N

H

H

N

H

H

H

N

H

arginine

Figure 1The major amino and imino acid residue constituents of collagen