Type I and type II collagen consist of a triple helix form with 3 alpha chains. Type I collagen has two alpha 1 chains and one alpha 2 chain, and type II collagen has three identical alpha chains.

Collagen in the tissue contains telopeptides at N-terminal and C-terminal of collagen. The telopeptides play roles to keep the collagen fibril structure by cross linkages with each other. However, when we solubilize collagen from tissues, we generally use pepsin which cleaves out the telopeptides. The collagen without telopeptides is called atelocollagen. Since the atelocollagen does not have high antigenicity, rather than telopeptides, the atelocollagen has been used for cosmetics and tissue engineering.

The native collagen forms always the triple helix form which is 300 kDa (alpha chain: 100 kDa x 3), but once it receives heating (higher than 42C), it turns into 3 individual alpha chains. This change sometimes makes scientists confusing.

In SDS-PAGE analysis, samples receive heating to denature samples. The collagen samples show three bands which are alpha chain, beta chain (two alpha chains cross-linked), and gamma chain (three alpha chains cross-linked), 100, 200 and 300kDa, respectively. (1)

1. E. J. Miller, R. K. Rhodes, Preparation and characterization of the different types of collagen. Methods Enzymol. 82 Pt A, 33–64 (1982).