SynopsisThe intrinsic viscosities at zero shear rate of defined complexes of proflavine, 9-aminoacridine, and g-amino-l,2,3,4tetrahydroacridine with calf thymus DNA have been determined at various ionic strengths by means of rotating cylinder viscometers. By controlled adjustment of the composition of the mixtures, the amount of bound acridine ( T moles/g.-atom DNA phosphorus) was maintained constant at different. dilutions. The intrinsic viscosities of the complexes increased with T up to r values (ca. 0.16-0.20) corresponding to the end of the process of strong binding of the acridinium cations. However, complex formation between the acridines and thermally denatured DNA caused either a marked decrease in viscosity (at the low ionic strengths of 0.0015 and 0.005) or no change a t all (ionic strength 0.1). These results are discussed in the light of presently available hydrodynamic theories relating the intrinsic viscosity of DNA to its molecular extension.When aminoacridines are bound to DNA in solution changes occur in the properties of the DNA solutions which suggest that the DNA has become more extended.'V2 This is consistent with an earlier observation3 of formation of a stable gel when enough positive cations of proflavine, 3,6-diaminoacridine1 were bound to DNA to neutralize all the negative charges on the DNA (r = 1). It has frequently been pointed out that the proflavine cations probably rest on the flat rings of the nucleic acid bases; for example, the ljgand molecules have to have a minimum flat area in order to be strongly bound.3 This strong binding (process I of Peacocke and Skerrett3) has a maximum limit of about 4 or 5 proflavine cations for every turn of the double helix (r 2 0.2-0.25). At higher concentrations of free proflavine, a weaker binding process (11) becomes dominant and appears to be chiefly dependent on proflavineproflavine interactions. Lermanl observed a marked increase in the viscosity of DNA solutions when acridines were bound, e.g., at r = 0.13-0.21, the viscosity increased by a factor of the order of three. Although a provisional interpretation of these increases in viscosity was attempted' it could not be securely based, since the observed viscosity values could not be reliably extrapolated to zero shear rate from the values observed at the lowest shear rate (ca. 30 see.-') obtained with capillary viscometers; 971
SynopsisSolutions of calf thymus DNA have been degraded in the presence of vibrating air bubbles in ultrasonic fields of low power which would not normally induce ultrasonic cavitation. The DNA was degraded to a limiting intrinsic viscosity, after which further irradiation by ultrasound had little or no effect. This limiting intrinsic viscosity decreased with increase in the ultrasonic intensity. Previously developed theories have been adapted to calculate the maximum velocity gradient associated with the streaming of the solution around such vibrating air bubbles. The tensile force which is induced and which acts on the DNA has been calculated on the basis of current theories of degradation by hydrodynamic shear. These calculation9 indicate that the degradation of the DNA by ultrasound under conditions of "stable cavitation" is mainly the result of the shearing forces engendered in the solution around the oscillating bubbles.
SynopsisSolutions of T7 bacteriophage or calf thymus DNA are degraded in solution by ultrasonic fields of low intensity in the presence of vibrating air bubbles but are not degraded at these low intensities when such bubbles are absent. Evidence is presented for the hydrodynamic nature of the observed degradation and theoretical simulation of a plausible degradation mechanism is compared with experimental degradation studies. It is concluded that degradation of such linear macromolecules as DNA may occur as a result of stresses induced in the macromolecule; these stresses are the result of a relative movement of solvent molecules and the macromolecules in the time-independent flow of solvent near the vibrating bubbles.DiYA from bacteriophage T7 was extracted by a slight modification of the method of Nandel and Hershey5 and had an extinction per mole of phosphorus at 259 m M of 6500.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.