Interaction of DNA and deoxyribonucleoprotein with methylene blue after the treatment with fixation solutions used in chromosome G-banding techniques.

Maximum binding capacity of calf thymus DNA and deoxyribonucleoprotein for methylene blue was investigated. The binding capacity of native and heat-denatured solutions of the biopolymers was compared with that of the solutions incubated with fixatives used in cytology, viz. 4% formaldehyde and methanol-acetic acid (3 : 1) mixture. The binding capacity of DNA and DNP is strongly reduced after the treatment with both fixation agents. Thermal denaturation leads to a small decrease in the binding capacity of DNA, but does not influence that of DNP. These results were compared with microphotometric determination of nuclear methylene blue content in thymocyte spreads. Fixation with MeAc increased the dye content as compared with air-dried thymocytes, whereas 4% formaldehyde exhibited practically no influence. The mechanisms connected with the different staining properties after incubating with fixation agents DNA and DNP solutions on the one hand and the nuclear material of thymocyte spreads on the other hand are discussed.