Enzymatic method of incorporation of 125I into DNA

DNA can be labeled with iodine in the reaction catalyzed with lactoperoxidase. Iodine is incorporated in cytosine similarly as in the chemical reaction. Iodination by means of the enzymatic method is faster than by means of the chemical method. The equilibrium state is still achieved after 10 minutes, during the enzymatic reaction, while during the chemical reaction it is achieved after 30 minutes. The preservation of the proper concentration of LP/DNA less than or equal to 0.075. ensures the proper reaction rate and decreases "self-iodination" of the enzyme. Deviations from the optimum conditions of the enzymatic reaction cause the decrease of the iodine incorporation or the increase of degradation of nucleic acid. Labeled DNA (less than or equal to 10% ICl) slightly differs from non-labeled DNA. Labeling 10% cytosine in DNA causes the decrease of melting temperature of about 1 degree C. DNA labeled this way reassociates with homologous non-labeled DNA at approximately 98%.