Type VI collagen is composed of a 200 kd subunit and two 140 kd subunits

We have isolated type VI collagen, a transformation-sensitive glycoprotein of the extracellular matrix, in an intact, disulfide-bonded form. The protein contains a 200 kd subunit and two different 140 kd subunits in a stoichiometric ratio. Based on the amount of hydroxyproline and hydroxylysine, the sensitivity to bacterial collagenase and the cross-reactivity with antibodies to pepsin-extracted type VI collagen, we have identified the 200 kd subunit as the alpha 3(VI) chain and the two 140 kd subunits as the alpha 1(VI) and alpha 2(VI) chains. The alpha 3(VI) chain is synthesized by cells in culture as a precursor of 260 kd, while no precursor form of the other two chains could be detected.