Abstract: The molecule of C1027,an antitumor antibiotic with extremely potentcytotoxicity against cultured cancer cells ,is composed of an enediyne chromophore and an apoprotein of 10.5 kDa.These two parts of the molecule,connecting each other through non-covalent binding,can be dissociated and reconstituted.As determined by clonogenic assay,the chromophore served asthe active part of the molecule,displaying potent cytotoxicity similar to that of intact C1027.Theactivity of free chromophore decreased more rapidly than that of intact C1027,indicating thatapoprotein played a role in protecting the chromophore from inactivation.By incubating together inphosphate buffer ,the chromophore and apoprotein were reconstituted to form an intact C1027.Theratio of chromophore and apoprotein remained 1 :1 in the reconstituted molecule ,even though extraamount of chromophore was added.The optimal condition for the reconstitution was pH 7.0 ,at 20℃for 12 h.When the disulfide bond of the apoprotein was reduced by DTT ,the activity of C1027decreased more rapidly.C1027 was digested by pronase and the produced fragments of variousmolecular weights were examined by capillary electrophoresis.The cytotoxicity of 3～5kDa fragmentapproximated that of intact C1027 and its IC50 value was 0.07 fmol·L^-1.The results indicate thatthe intactness of the apoprotein is not indispensable for stabilizing the chromophore and a smallermolecule of 3～5kDa consisting of a peptide fragment and a chromophore may retain full C1027activity.