Process for preparing purified dimer of bone-derived factor

A process for the production of a purified dimeric bone morphogenetic factor which comprises subjecting an inclusion body of a bone morphogenetic factor to the following steps a)-c) in order, thereby producing the dimeric bone morphogenetic factor;

• a) introducing a polynucleotide encoding a bone morphogenetic factor into E. coli expressing said bone morphogenetic factor in the form of an inclusion body in E. coli, recovering (and washing) said inclusion body and treating it with a denaturing agent to obtain a solubilized monomer,
• b) treating the solubilized monomer without purification directly with a refolding solution in a final protein concentration from 1.6 mg/ml up to 5 mg/ml to obtain a dimeric bone morphogenetic factor,
• c) subjecting the dimeric bone morphogenetic factor to purification.