Labeling of ribosomal ribonucleic acid with iodine 125I

RNA was labeled with iodine in the reaction catalyzed with lactoperoxidase (LP). Labeling of RNA requires additional purification of LP on Sephadex G-100 and application of RNase inhibitors. Immobilized LP shows lower activity than a soluble enzyme but still it is sufficient to label RNA to 7% IC. Immobilized enzyme is easy to remove from the post-reaction mixture and can be used many times. Optimum conditions for enzymatic labeling were as follows: concentration ratio C/KI for the soluble enzyme equal to 7.5 (for the immobilized enzyme--12). The oxidizing agent (H2O2) used in the enzymatic method of labeling at the concentrations required in the reaction (3.5 X 10(-5) M) does not cause the degradation of nucleic acids as opposed to the oxidizing agent (TlCl3) used in the chemical method. The degree of RNA degradation increases with the amount of incorporated iodine. The RNA preparations of high degree of labeling (10% iodocytosine) by means of the chemical and enzymatic methods do not differ much. At lower labeling the enzymatic method produces less degraded preparations.