1. The interaction between quinacrine mustard and mononucleotides and polynucleotides was investigated by fluorimetry and absorbance spectrophotometry. 2. The fluorescence spectrum of quinacrine mustard is independent of the ionic strength and pH. The dependence of the quinacrine mustard fluorescence intensity on ionic strength, pH and anions is described. 3. The fluorescence intensity of quinacrine mustard was enhanced with the mononucleotide adenylic acid and polynucleotides such as poly(rA), poly(rU) and poly(rA,rU). 4. Quenching of the fluorescence intensity of quinacrine mustard occurred with the mononucleotide guanylic acid and with poly(rG) and poly(rC,rG). 5. The mononucleotide cytidylic acid or poly(rC) showed no effect on the fluorescence intensity of quinacrine mustard. 6. The interaction between the dye and native DNA species was also dependent on the presence of base-specific binding sites in the DNA. The higher the (G+C) content was in the native DNA tested the higher was the quenching effect on the fluorescence intensity of quinacrine mustard. 7. No interaction was found between the dye and methylated DNA. The binding between quinacrine mustard and apurinic DNA was confirmed to be in the phosphate groups of the purines.
The quantity of antibodies to double-stranded DNA (ds-DNA) in 53 pleural effusions from 48 patients was measured by means of a modified Farr technique. In 10 samples, binding of ds-DNA was greater than 5 mg/l (range 6--14 mg/l), five samples being from patients with systemic lupus erythematosus (SLE), four from patients with lung cancer, and one from a patient with pulmonary tuberculosis. After treatment of pleural effusion samples with DNase, there was a marked increase of ds-DNA binding in the SLE group (n = 5), but none in the lung cancer group (n = 7) or in 4 patients with pleural effusions of various origin. In pleural fluid, demonstration of antibodies to ds-DNA and anti-ds-DNA-ds-DNA complexes, unmasked by DNase, may prove valuable when differentiating clinical conditions with pleural effusions.
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