The component alpha-chains of type V collagen from bovine bone were isolated and structurally characterized by gel electrophoresis, high performance liquid chromatography (HPLC) and amino acid sequence analysis. Three distinct alpha-chains were identified. Two of these were the well described alpha 1 (V) and alpha 2 (V) chains; the third proved to be identical to the cartilage alpha 1 (XI) chain. In adult bone the ratio between the three chains was about 1:1:1. Native type V collagen was cleaved by trypsin at 33 degrees C or 37 degrees C into 3/5 fragments. Aminoterminal sequence analysis of the alpha 1 (V) and alpha 1 (XI) fragments showed they both resulted from trypsin cleavage between residue 434 and 435. Trypsin apparently cleaves the type V molecule within a relatively unstable domain of the triple helix which presumably may also be a natural site of initial cleavage by a protease in vivo.