To investigate the properties of the neomycin-hammerhead interaction,
inhibition of hammerhead activity was measured as a function of magnes
ium concentration and pH. The data are consistent with a simple compet
ition between magnesium and neomycin with about five magnesium ions re
quired to displace neomycin from the hammerhead. The pH dependence of
the inhibition of hammerhead cleavage by neomycin and two related amin
oglycosides was also determined. The data indicate that at least three
of the five positively charged ammonium ions present on neomycin are
critical for inhibiting hammerhead function. Taken together, these res
ults suggest that the neomycin-hammerhead interaction is mostly ionic
in character.