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Physical and chemical properties of human type III procollagen.

Type III procollagen was isolated from the serum-free culture media of human foreskin fibroblasts by adsorption to controlled-pore glass beads and chromatography of the eluted procollagen pool on diethylaminoethylcellulose [Gerard, S., & Mitchell, W. M. (1979) Anal. Biochem. 96, 433-447]. Sodium dodecyl sulfate (NaDodSO4) electrophoresis in 1% agarose-2% acrylamide gels with or without prior sample reduction revealed the predominance of a band with retarded mobility as compared to human procollagen I [hupro(I)]. Digestion of hupro(III) with pepsin yielded a product whose electrophoretic mobility was retarded for both the intact trimer and its reduced monomeric subunit as compared to that for the respective bands of rat skin (type I) collagen. NaDodSO4-polyacrylamide gel electrophoresis of bacterial collagenase-digested hupro(III) demonstrated disulfide-bonded propeptides which upon reduction were replaced by two distinct monomeric propeptide bands. The amino acid composition of hupro(III) was similar to that of hupro(I) but contained increased amounts of HO-Pro and Cys and less Thr, Ala, Val, and Arg. Sedimentation equilibrium analysis in 1 M CaCl2 yielded at extrapolated zero concentration a Mr of 505 +/- 25K. A [hupro(III) - collagen(III)] circular dichroic difference spectrum suggests approximately 10% alpha helix. The zero-order mutarotation rate of hupro(III) (vo = 55.0 X 10(-5) s-1) was twice that of hucol(III) (vo = 25.4 X 10(-5) s-1) at 20 degrees C, which may reflect the influence of the interchain disulfide-bonded carboxyl propeptides on the process of collagen fold formation.