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Biophysical Journal 86:1012-1017 (2004)
© 2004 The Biophysical Society

Binding of meso-Tetrakis(N-methylpyridinium-4-yl)porphyrin to AT Oligomers: Effect of Chain Length and the Location of the Porphyrin Stacking

Jin-Ok Kim *, Young-Ae Lee *, Byeong Hwa Yun *, Sung Wook Han {dagger}, Sam Tag Kwag {ddagger} and Seog K. Kim *

* Department of Chemistry, Yeungnam University, 214-1 Dae-dong, Kyoungsan City, Kyoung-buk 712-749, Republic of Korea; {dagger} Department of Environmental Engineering, Kyoungwoon University, Sangdong-myun, Kumi, Kyoung-buk 136-701, Republic of Korea; and {ddagger} Division of Chemical Engineering, Pukyong National University, Busan 608-739, Republic of Korea

Correspondence: Address reprint requests to Seog K. Kim, Tel.: +82-53-810-2362; Fax: +82-53-815-5412; E-mail: seogkim{at}yu.ac.kr.

Circular dichroism (CD) spectra of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) that are associated with various duplex and triplex AT oligomers were investigated in this study. A strong positive CD was apparent for both the TMPyP complexed with duplex d[(A-T)12]2, d(A)12·d(T)12 and triplex d(A)12·d[(T)12]2 at a low mixing ratio. As the mixing ratio increased, bisignate excitonic CD was produced for TMPyP complexed with duplexes, whereas the positive CD signal remained the same for the TMPyP-d(A)12·d[(T)12]2 complex. This difference in the CD spectrum in the presence of duplex and triplex oligomers indicates that the moderate stacking of TMPyP occurs at the major groove of the duplex and the monomeric binding occurs in (or near) the minor groove. When TMPyP forms a complex with duplex d[(A-T)6]2 only excitonic CD was observed, even at a very low mixing ratio. Therefore, at least seven or more basepairs are required for TMPyP to exhibit a monomeric CD spectrum. After close analysis of the CD spectrum, the TMPyP-poly[d(A-T)2] complex could be explained by a combination of the CD spectrum of the monomeric, moderately stacked, and extensively stacked TMPyP.






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Copyright © 2004 by the Biophysical Society.