The precise role of the alpha(2)-chain in collagen type I is of considerable scientific interest. Our recent studies demonstrated that the most noticeable difference between type I collagens, which were obtained from bovine hard tissues (bone, dentine) and soft tissues (tendon, skin), was presented in the position of beta chain dimers using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The additional band observed both in the bone and dentine collagen was putatively identified as beta(22) dimer (made of by an intermolecular cross-linking between two alpha(2)-chains). Further investigations carried out on bovine bone and skin collagen, corresponding to hard tissue and soft tissue collagen respectively, confirmed this hypothesis. Successful separation of individual beta(22) dimer from bone collagen was achieved. The procedure involves molecular-sieve chromatography on a Sephacryl S-400 column followed by differential acetone precipitation. Identification was done by the widely used methods, such as SDS-PAGE and cyanogen bromide (CNBr)-cleaved peptide analysis. It was proposed that the dimer and consequently alpha(2)-chains may play important roles in the morphological and biological differences between hard and soft tissues. (c) 2007 Published by Elsevier Ltd.