DNA and Double-Stranded Oligonucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 415

Table 12 .17. Rate constants (unit: dm 3 mol −1 s −1 ) of the reaction of Hoechst 3342 with some
nucleotide-derived radicals. (Adhikary et al. 1997b)

Radical Rate constant

CMP-derived peroxyl radicals

7 × 10 6

9 × 10 6 TMP-derived peroxyl radicals

1.7 × 10 9

GMP-derived radicals

AMP-derived radicals

2.1 × 10 9

The binding kinetics and equilibrium constants for five different (A/T) 4 DNA
sites have been studied in detail, showing that the binding kinetics are complex
(Breusegem et al. 2002). Further information as to Hoechst binding by DNA has
been obtained by f fluorescence spectroscopy (Adhikary et al. 2003) and, to some
extent, by atomic force microscopy (Zareie et al. 1998).
In aqueous solution, intercalated Hoechst 3342 protects DNA against strand
breakage beyond • OH-scavenging (quenching diameter by Hoechst 3−4 bp; Ad-
hikary et al. 1997a). Besides, intercalated Hoechst reacts with • OH-induced DNA
on the ms time scale. The Hoechst -reactive damaged DNA sites are likely the
oxidizing radicals A • and G • and pyrimidine peroxyl radicals (Table 12.17; for
further pulse radiolysis studies on Hoechst in aqueous solution see Adhikary et
al. 2000).

12 .11. 4
Small Proteins and Polyamines

Various reasons have been put forward as to why the spore is less sensitive to
H 2 O 2 than the vegetative cell. In the spore, the DNA is covered by the so-called
small acid-soluble proteins (SASP) instead of water which makes it relatively in-
accessible to oxidative damage as these SASPs may provide compaction besides
sacrificial protection (e.g., Setlow 1994, 1995; Setlow and Setlow 1993).
Polyamines are ubiquitous cell components essential for normal growth and
may be targets for therapeutic intervention (Marton and Pegg 1995). The pro-
tecting effects of polyamines is even more pronounced than that of proteins,
such as, for example, the bacterial MC1 protein or the lac suppressor to their
binding sites (Isabelle et al. 1993, 1999). Multiply protonated polyamines such