A small dermatan sulphate proteoglycan (DSPG) was extracted from rat cervices and was purified by using DEAE-Sephacel ion-exchange chromatography, gel filtration on Sepharose CL-2B and CsCl-density-gradient centrifugation. Sedimentation-equilibrium centrifugation gave a weight-average Mr of 95,000. Amino acid analysis showed a high content of aspartic acid, glutamic acid, glycine and leucine. The glycosaminoglycan chains had Mr 50,000 as determined by gel filtration. Chondroitin AC lyase and chondroitin ABC lyase digestions of these chains showed that they were composed of 75% dermatan sulphate and 25% chondroitin sulphate. Chondroitin ABC lyase digestion produced a core protein of Mr 45,000. The core protein, after treatment with HF, had Mr 37,000. Amino acid sequences of the N-terminus and a CNBr-cleavage peptide showed similarity to the sequences of core proteins of small proteoglycans of bovine and human origin, but the N-terminal glycosaminoglycan-attachment site (Ser-Gly-Ile-Ile) differed from the consensus sequence (Ser-Gly-Xaa-Gly) [Bourdon, Krusius, Campbell, Schwartz & Ruoslahti (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 3194-3198]. A polyclonal antibody against the rat cervical DSPG reacted with small proteoglycans from cervices of human, mouse, dog, cow and sheep. DSPG is the major proteoglycan species present in the cervix. The amount of DSPG per cervix increases 4-fold during pregnancy, then falls precipitously within 1 day post partum. A role in cervical dilatation is postulated for this proteoglycan.

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