Identification of nondisulfided proα₁(IV) chain produced by cultured B16 melanoma cells

Two collagenous polypeptides with apparent molecular weights of 180 and 500 kDa under a nonreducing condition were found to be produced in the culture medium of B16 mouse melanoma cells. Under a reducing condition, the higher molecular weight polypeptide (500 kDa) migrated at an identical position to the 180 kDa polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both polypeptides were found to have an identical primary structure by V8 protease peptide mapping. Cyanogen bromide cleavage patterns, the fragments produced by pepsin digestion, and partial amino acid sequences of the 180 kDa polypeptide were compatible with those of proα₁(IV) chain. These results indicate that B16 mouse melanoma cells preferentially produce proα₁(IV) chains consisting of two forms: disulfide- and nondisulfide-bonded forms.