THE CUB DOMAINS OF PROCOLLAGEN C-PROTEINASE ENHANCER CONTROL COLLAGENASSEMBLY SOLELY BY THEIR EFFECT ON PROCOLLAGEN C-PROTEINASE BONE MORPHOGENETIC PROTEIN-1/

Procollagen C-proteinase enhancer (PCPE) is a 55 kDa glycoprotein that increases the activity of procollagen C-proteinase (PCP)/bone morphog enetic protein-1 (BMP-1) during C-terminal processing of fibrillar col lagen precursors. Here we show that the 36 kDa, active fragment of PCP E enhances the activity of both the short (mouse) and long (chick) for ms of PCP/BMP-1. The activity of PCPE is not associated with the forma tion of sedimentable procollagen aggregates. In addition, PCPE (36 kDa ) has no effect in vitro on N-terminal procollagen processing by highl y purified procollagen N-proteinase. Finally, when the amount of PCP i s adjusted so that the rate of C-terminal processing remains constant, PCPE (36 kDa) has no effect on the assembly of collagen or pN-collage n in vitro following C-terminal processing of the corresponding precur sors.