TY - JOUR
T1 - Orientation and Linear Dichroism Characteristics of Porphyrin-DNA Complexes
AU - Geacintov, Nicholas E.
AU - Ibanez, Victor
AU - Rougee, Michel
AU - Bensasson, Rene V.
PY - 1987
Y1 - 1987
N2 - The linear dichroism spectra of complexes of tetrakis(N-methyl-4-pyridinio)porphine (H2TMpyP) and its zinc(II) derivative (ZnTMpyP) with DNA oriented in a flow gradient have been investigated. The dichroism of H2TMpyP determined within the Soret band and the Qyband system is consistent with an intercalative conformation in which the plane of the porphyrin ring system is nearly parallel to the planes of the DNA bases. In the case of ZnTMpyP on the other hand, the porphyrin ring system is inclined at angles of 62-67° with respect to the axis of the DNA helix. The pyridyl groups in both cases are characterized by a low degree of orientation with respect to the axis of the helix. In contrast to H2TMpyP which does not significantly affect the degree of alignment of the DNA in the flow gradient, the binding of ZnTMpyP causes a significant decrease (about 50% for a base pair/ZnTMpyP ratio of 20) in the intrinsic dichroism at 260 nm due to the oriented DNA bases; the binding of ZnTMpyP to DNA either gives rise to regions of higher flexibility or causes bends or kinks at the binding sites. Increasing the ionic strength has little influence on the linear dichroism of the ZnTMpyP-DNA complexes, but the number of molecules bound at intercalation sites diminishes in the case of the H2TMpyP-DNA complexes; the accompanying changes in the linear dichroism characteristics suggest that external H2TMpyP complexes are formed at the expense of intercalation complexes. Taken together, these linear dichroism results are consistent with the intercalative model for H2TMpyP-DNA and the external binding model for ZnTMpyP-DNA complexes proposed by Fiel et al. [Fiel, R. J., Howard, J. C., & Datta Gupta, N. (1979) Nucleic Acids Res. 6, 3093–3118] and Pasternack et al. [Pasternack, R. F., Gibbs, E. J., & Villafranca, J. J. (1983) Biochemistry 22, 5409–5417].
AB - The linear dichroism spectra of complexes of tetrakis(N-methyl-4-pyridinio)porphine (H2TMpyP) and its zinc(II) derivative (ZnTMpyP) with DNA oriented in a flow gradient have been investigated. The dichroism of H2TMpyP determined within the Soret band and the Qyband system is consistent with an intercalative conformation in which the plane of the porphyrin ring system is nearly parallel to the planes of the DNA bases. In the case of ZnTMpyP on the other hand, the porphyrin ring system is inclined at angles of 62-67° with respect to the axis of the DNA helix. The pyridyl groups in both cases are characterized by a low degree of orientation with respect to the axis of the helix. In contrast to H2TMpyP which does not significantly affect the degree of alignment of the DNA in the flow gradient, the binding of ZnTMpyP causes a significant decrease (about 50% for a base pair/ZnTMpyP ratio of 20) in the intrinsic dichroism at 260 nm due to the oriented DNA bases; the binding of ZnTMpyP to DNA either gives rise to regions of higher flexibility or causes bends or kinks at the binding sites. Increasing the ionic strength has little influence on the linear dichroism of the ZnTMpyP-DNA complexes, but the number of molecules bound at intercalation sites diminishes in the case of the H2TMpyP-DNA complexes; the accompanying changes in the linear dichroism characteristics suggest that external H2TMpyP complexes are formed at the expense of intercalation complexes. Taken together, these linear dichroism results are consistent with the intercalative model for H2TMpyP-DNA and the external binding model for ZnTMpyP-DNA complexes proposed by Fiel et al. [Fiel, R. J., Howard, J. C., & Datta Gupta, N. (1979) Nucleic Acids Res. 6, 3093–3118] and Pasternack et al. [Pasternack, R. F., Gibbs, E. J., & Villafranca, J. J. (1983) Biochemistry 22, 5409–5417].
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U2 - 10.1021/bi00385a021
DO - 10.1021/bi00385a021
M3 - Article
C2 - 3607012
AN - SCOPUS:0023240881
SN - 0006-2960
VL - 26
SP - 3087
EP - 3092
JO - Biochemistry
JF - Biochemistry
IS - 11
ER -