FIGURE 3.

Analysis of Ile/Leu in the X-position of the α1 chain of types I-III collagen. Ile/Leu in the X-position can be classified into four categories by the distribution of imino acids (a): Ile/Leu immediately followed by a Hyp (O) in the Y position (Type I, green); Ile/Leu followed by two triplets at least one of which contains imino acids (Type II, cyan); Ile/Leu preceded by two triplets at least one of which contains no imino acids (Type III, red); other Ile/Leu with two preceding imino acid triplets and no imino acids in the Y position or in the following two triplets (Type IV, yellow) (b, c). There is only one Ile in the α1 chain of types I and III collagens and one Leu in type II collagen following the pattern IV (yellow) and they are the real collagenase cleavage sites.