Solubilized rat liver mitochondrial choline dehydrogenase was further purified by the SDS-PAGE and electroblotting methods. Both the lipids and detergents etc. were removed during the process of purification. The amino terminal sequence of the purified CDH was determined, it was: VAAAAGGGKD. Although the sequence showed high homology with mouse CO5 protein, rat adenylyl cyclase and human oxysterol-binding protein, there was no similarity with CDH of E.coli.