Q-b
and electron nucle
ar double reson
ance (ENDOR) h
as me
asured
anisotro
pic, dist
ance-de
pendentdi
pol
ar hy
perfine cou
plings from iron in ferric bleomycin[Fe(III)-BLM]
and in
activ
ated bleomycin [Act-BLM] to
31P of substr
ate DNA. Studies were focused onbleomycin com
plexes with
a self-com
plement
arydu
plex DNA 10-mer, d(GGAA
GCTTCC)
2, cont
aining
a5'-G-C-3' sequence th
at is selective for bleomycincle
av
age (M
ao, Q.; Fulmer, P.; Li, W.; DeRose, E. G.; Petering, D. H.
J. Biol. Chem. 1996,
271,6185-6191).Bleomycin com
plexes with high molecul
ar weight c
alf thymus DNAwere
also used. Fe(III)-BLM
and Act-BLM com
plexes with the 10-mer
and the c
alf thymus DNA showed
anisotro
pic
31P di
pol
ar hy
perfine cou
plingsfrom which
an Fe(III)-to-
31P dist
ance w
as estim
ated
at7.4 ± 0.2 Å. High-resolution,
angle-selected ENDORof the Fe(III)-BLM 10-mer com
plex showed th
at theFe(III)-to-
31P vector l
ay
at 25 ± 5
![](/im<font color=)
ages/entities/deg.gif"> to them
axim
al
gv
alue direction, where the l
atter direction
pointed ne
ar theexch
ange
able
protons on
axi
al BLM lig
ands
and is
associ
ated with the m
axim
al hy
perfine cou
plings of these
protons(
Veselov, A.; Sun, H.; Sienkiewicz, A.;T
aylor, H.; Burger, R. M.; Scholes, C. P.
J. Am. Chem. Soc.1995,
117, 7508-7512). Proton ENDORfe
aturesof the Fe(III)-BLM but not Act-BLM were
perturbed by DNAsubstr
ate. In the
presence of the 10-mer
andthe c
alf thymus DNA,
proton ENDOR reve
aled distinct
perturb
ation to thefrequencies of three sets ofnonexch
ange
able
protons
assigned to the BLM m
acrocycle
and estim
ated tobe 2.9-3.5 Å from Fe(III)
and tothe frequencies of exch
ange
able,
axi
ally loc
ated
protons. Incontr
ast, the hy
perfine cou
plings of cov
alentlybonded, first-shell nitrogen
and [
17O]
peroxy lig
andswere unch
anged.