Kinetic analysis of the in vitro binding of radioactive cis di chloro di ammine platinum ii and trans di chloro di ammine platinum ii to dna

Johnson, N.P.; Hoeschele, J.D.; Rahn, R.O.

Chemico-Biological Interactions 30(2): 151-170

1980


ISSN/ISBN: 0009-2797
Accession: 005780179

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Abstract
The binding of cis(c)- and trans(t)-Pt(NH3)2Cl2 DNA at PtDNA nucleotide ratios (Ri) of 0.1 or less was studied by radioactive 195mPt-labeled compounds. Kinetic data are consistent with the following scheme: .**GRAPHIC**. At 25.degree. C and pH 5-6 in 5 mM NaCLO4, the values for the rate constants in the above scheme for the c-isomer are k2 = 2.2 .times. 10-5 s-1, k7 = 0.32 (s M)-1 and k8 = 143 (s M)-1; for the t-isomer the values are k2 < 0.5 .times. 10-5 s and k7 = 0.95 (s M)-1. Pt-DNA adducts do not undergo detectable exchange after 3 days at 37.degree. C, indicating the absence of a dynamic equilibrium. For both isomers the rate of binding is the same for single- and double-stranded DNA. The conclusions derived from Ag+ and H+ titration studies are consistent with binding at guanine N(7) for Ri < 0.1. The reaction rate is competitively inhibited by various salts and buffers and is suppressed by raising the pH (50% inhibition of initial rates at pH 7.3). At 37.degree. C and pH 7 in 0.15 M NaCl, 6-8% of the c- and t-isomers bind to DNA in 24 h, suggesting that both compounds hould bind to DNA under biological conditions.