CHARACTERIZATION OF MONOMERIC AND HOMODIMERIC FORMS OF OSTEOCLASTOGENESIS INHIBITORY FACTOR

Osteoclastogenesis inhibitory factor (OCIF) is present naturally as tw o molecular forms, a monomer and a homodimer. The two forms of recombi nant human OCIF (rOCIF) produced by Chinese hamster ovary (CHO) cells were purified to homogeneity. Determination of the C-terminal amino-ac id sequences of the two forms of rOCIF revealed that the monomeric rOC IF lacked several amino acids including Cys(379), which is involved in the intermolecular disulfide bond, in its C-terminal region. The two forms of rOCIF were indistinguishable in stability, sialic acid conten t, and specific activity in inhibition of osteoclastogenesis. In contr ast, the homodimeric rOCIF was stronger in heparin-binding ability tha n the monomeric rOCIF. The homodimeric rOCIF was significantly shorter in initial half-life and smaller in AUC value in rats than the monome ric rOCIF, but exerted more potent biological activity in reducing the calcium concentration in serum of rats than did the monomeric rOCIF. (C) 1998 Academic Press.