Helical structures from neutral biopolymers - Physical Gels from Biological and Synthetic Polymers - page 184

Table 7.1 Imino acid composition and denaturation temperatures of collagens from various sources.

Imino acid (wt%) Cod Ling Portuguese dogsh Megrim Tuna Calf skin

Pro 10.3 10.9 11.2 12.8 12.4 13

Hyp 7.1 6.9 7.5 9.1 9.2 12.2

Pro +Hyp 17.4 17.8 18.7 21.9 21.6 25.2

T m (°C) 15 19.5 20.9 27.9 28.8 36

(a)

(b)

(c)

(d)

Structure of collagen fibres: (a) fibres are bundles of twisted fibrils; (b) fibrils are made of
rods arranged in parallel and staggered arrays (periodic spacing 64 nm); (c) each rod is a
right-handed triple helix; (d) the single collagen strand is a left-handed helix.

Figure 7.1

supramolecular arrangement of the collagen rods in fibrils is called the quaternary

structure. The fibres are strengthened by covalent bonds and thus are insoluble. The

hierarchical arrangement of collagen in the native state is shown in Figure 7.1 . At larger
scales, in tissues, the assemblies of fibres form a wide variety of patterns.

7.2.3 Amino acid composition in collagens from various sources: mammalian and fish

Mammalian collagens are the most common, but other sources have been exploited,
including those from piscine sources, particularly skins. The main difference between
mammalian and fish collagens lies in their imino acid composition ( Table 7.1 ). In

contrast to mammalian collagens, the content of these particular imino acids in

sh

collagens varies signi cantly in the range 17 - 22 wt%, while in mammalian collagens it

is close to 25 wt%.
Fish are non-homoeothermic, and it was recognized that the denaturation temperatures
of the various collagens parallel the natural environment temperatures of the species from