A novel enzymatic reaction for converting DNA to CO-DNA.

We have found previously that DNA from both the chick cerebrum and cardiac muscle has a modified structure. We named this novel DNA, CO-DNA. CO-DNA is a form of DNA in which a carbonyl group is attached to C-1 of the 2-deoxyribose and to the nitrogenous base. Therefore, 3-deoxyglucosone is the sugar constituent for CO-DNA. We found previously that the modification of the sugar moiety in DNA occurs around embryonic day 12 in the chick embryo. In this study, we isolated enzymes for the conversion of DNA to CO-DNA from chick cerebra. In our reaction system, uniformly labeled 14C-glucose was used as substrate. During incubation, the radioactivity was incorporated into DNA. From the analysis of 14C-labeled deoxynucleoside, the radioactive sugar was confirmed to be 3-deoxyglucosone. We propose a series of reactions involved in the conversion of DNA to CO-DNA: (1) DNA-enzyme complex is formed during preincubation, (2) 14C-glucose is transformed to 14C-3-deoxyhexonic acid, (3) 14C-3-deoxyhexonic acid is subsequently transformed into the sugar-phosphate, which is a mixture of phosphorylated 14C-3-deoxyhexonic acid and phosphorylated 14C-3-deoxyglucosone, (4) 2-deoxyribose in DNA is replaced with 14C-3-deoxyglucosone through its intermediate phosphorylated form, and (5) DNA is finally converted to CO-DNA.