Open AccessPreferential Interstrand Cross‐Linking of DNA Rich in Guanine and Cytosine by cis ‐Dichlorodiammineplatinum(II)
Author(s) -
GANGULI Prasanta K.,
THEOPHANIDES Theophile
Publication year - 1979
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1979.tb19729.x
Subject(s) - hyperchromicity , bathochromic shift , dna , absorbance , cytosine , chemistry , guanine , platinum , stereochemistry , crystallography , biochemistry , chromatography , nucleotide , physics , quantum mechanics , fluorescence , gene , catalysis
Two native DNAs differing in G + C content were bound equally with the antitumour drug cis‐ Pt(NH 3 ) 2 Cl 2 at increasing Pt/P ratios. Resulting changes in their ultraviolet absorption spectra show equal fractional decreases in the initially different values of A 250 / A 270 for the two DNAs, and less prominent bathochromic and hyperchromic shifts for DNA richer in G + C. Changes in the absorbance ( A 260 ) observed before and after subjecting the DNA samples to the conditions of denaturation (with alkali) and renaturation, indicate the following effects of the platinum binding. Maximum renaturation occurs at 50% lower Pt/P ratio of 0.03 for Micrococcus lysodeikticus DNA (72% G + C) than 0.06 for salmon sperm DNA (41% G + C) and is maintained at higher Pt/P ratios. Interstrand cross‐links that facilitate renaturation, cause an incomplete melting of DNA so that the platinum‐DNA complex at pH 12.5 has a reduced absorbance. This effect is more evident for the platinum complex with DNA richer in G + C due to more interstrand cross‐links. Platinum‐induced destabilisation of DNA, shown by its hyperchromicity at the pre‐melting state (pH 6–7, 25°C) and also by a lowering of the pH corresponding to the mid‐point of its melting, is less evident for DNA richer in G + C.