ruthenium hexamine [Ru(NH3)6]3+ (generally used as an enzymereducing agent), on the activity of CChMVd-HHR was tested and the
results are compared in Fig. 5A. These two molecules are rather good
inhibitors of the ribozyme, with IC50 of 84 ± 6 μM and 25 ± 3 μM re sp ec ti ve ly . In s pi te of th e fac t th at th es e two mo le c ul es be a r th re e
positively charged amino groups, ruthenium hexamine appears to be
3. 5 ti me s mo re effi c ie nt a s in h ib it or of th e ri bo z yme th a n c ob a lt
hexamine. This result shows not only that the inhibition of CChMVdHHR self-cleav age is due to the positi vely-charg ed amino groups but
a ls o th a t it is m et a l- co re de pe n de n t, su gg es ti n g th at th e ru the n iu m
hexamine either can bind to an additional site(s) unreachable by the
cobalt hexamine or binds to the same site(s) with a higher affi nity. It
is in te re s ti ng t o re la te th is ob s er va ti on wi th th at of a st ud y of th e
infl ue n c e of th e in n er co or di n a ti on sp he re of c ob a lt a nd ru the ni u m
h ex a mi n e on the ir in t er ac ti on wi th th ym us DNA in so lu ti on . Th is
st ud y sh ow ed th at th e h yd ro dy n a mi c ra di u s of ru th en iu m is muc h
la rg er th an th a t of c ob a lt [ Rh ( Co 3) = 6 5 ± 5 nm a n d Rh ( Ru 3 ) =
440 ± 30 nm] although the two compounds exert an identical global
infl uence on the structure of the macromolecule [30].