Presence of high molecular weight forms of BMP-2 in early Xenopus embryos

Using polyclonal antibodies which recognize 18 kDa BMP-2, we have previously demonstrated that the major BMP-2 protein in Xenopus embryo extracts is monomeric and not dimerized whereas, the mammalian counterpart derived from bone extract was purified as a dimeric protein. In this study, the same antibodies (Ab383) were used to detect high molecular weight forms of Xenopus BMP-2. Partial purification of the immunoreactive 18 kDa BMP-2 from Xenopus embryo extract by gel filtration, heparin-Sepharose affinity chromatography and preparative SDS-PAGE resulted in co-purification and identification of higher molecular forms of BMP-2 of 110 kDa and 36 kDa. Diagonal SDS-PAGE analysis suggested that they are homodimer and multimer of the 18 kDa species, respectively, linked through disulfide bridge(s).