Characterization of the procollagen IV cleavage products produced by a specific tumor collagenase

The specific mammalian collagenase isolated from cultures of metastatic mouse PMT sarcoma cells cleaves murine procollagen IV into two segments, of approximate mass ratio 3:1. These fragments were separated by velocity sedimentation, visualized by electron microscopy, and analyzed. The longer COOH-terminal procollagen segment has a 270-nm collagenous portion with a knob at one end. This knob consists of the three previously identified, noncollagenous carboxyl propeptides, of approximately 30,000 daltons each. These carboxyl propeptides are chain-specific, and the three chains of each segment have the same amino to carboxyl orientation. The collagenase cuts through all three chains at one site, and the three-component chains of both the longer COOH-terminal procollagen segment and the shorter NH2-terminal procollagen segment are linked by interchain disulfide bridges. The enzyme cuts off the same COOH-terminal procollagen segment from procollagen IV monomers and tetramers, and the flexibility of this segment is similar to that of interstitial collagen helices. The amino ends of the NH2-terminal procollagen segments derived from tetramers remain joined as the 32-nm long "7 S collagen" junctional complex, and the remaining 89-nm long projecting threads are significantly more flexible than the COOH-terminal procollagen segment. The electrophoretic mobilities of the enzyme cleavage products are consistent with a heterotrimeric composition of this procollagen IV.