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CHEMICAL STUDIES ON AN ACRIFLAVINE-PHOSPHOTUNGSTATE COMPLEX; STAINING OF PHAGE DEOXYRIBONUCLEIC ACID MOLECULES FOR THE ELECTRON MICROSCOPE
1 Department of Anatomy, Harvard Medical School, Boston, Massachusetts 02115, Department of Biophysics, The Johns Hopkins University, Baltimore, Maryland 21218 and Laboratory for Electron Microscopy, ETH Universitätstrasse 2, Zürich, Switzerland
Electrophoretic studies showed that the acriflavine-phosphotungstate (A-PTA) complex, which was formed by the reaction of acriflavine with phosphotungstic acid (PTA), contained a lower net positive charge than neutral acriflavine alone. Spectral studies from the titrations of specified aliquots of acriflavine with increasing volumes of PTA showed that the formation of A-PTA was characterized by a shift of the absorption peak of acriflavine from 452 mµ to a lower wavelength, at 446 mµ. The saturation of PTA binding sites on the acriflavine occurred when 3 molecules of dye reacted with 1 molecule of PTA. Binding curves of both neutral acriflavine and of A-PTA with "native" and with heat-denatured DNA showed shifts of 
max to longer wavelengths. A-PTA bound less native and less denatured DNA than the dye alone. The coupling of acriflavine with PTA caused a decrease in the net ability of the A-PTA complex to bind DNA. Double stranded DNA molecules from T3 bacteriophage were stained with the A-PTA complex for the electron microscope.
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