The collagen in lung is heterogeneous; these are probably five different types of collagen chains synthesized in lung. The tracheobronchial tree synthesizes alpha 1(II) chains and the peripheral lung synthesizes at least alpha 1(I) and alpha 2 chains. Additional evidence suggests the lung also synthesizes alpha 1 (III) chains and possibly alpha 1(IV) (basement membrane) chains. These different collagen chains have distinct primary amino acid sequences as demonstrated by cyanogen bromide peptide mapping.