Metal-phosphate interactions in the hammerhead ribozyme observed by 31P NMR and phosphorothioate substitutions.

The hammerhead ribozyme is a catalytic RNA that requires divalent metal cations for activity under moderate ionic strength. Two important sites that are proposed to bind metal ions in the hammerhead ribozyme are the A9/G10.1 site, located at the junction between stem II and the conserved core, and the scissile phosphate (P1.1). (31)P NMR spectroscopy in conjunction with phosphorothioate substitutions is used in this study to investigate these putative metal sites. The (31)P NMR feature of a phosphorothioate appears in a unique spectral window and can be monitored for changes upon addition of metals. Addition of 1-2 equiv of Cd(2+) to the hammerhead with an A9-S(Rp) or A9-S(S)(Rp) substitution results in a 2-3 ppm upfield shift of the (31)P NMR resonance. In contrast, the P1.1-S(Rp) and P1.1-S(Sp) (31)P NMR features shift slightly and in opposite directions, with a total change in delta of

Activities and relative affinities of divalent metals in unmodified and phosphorothioate-substituted hammerhead ribozymes.

The roles of metals in the phosphodiester bond cleavage reaction performed by the hammerhead ribozyme are under investigation. In this study, the apparent affinities and the abilities of several different metals to support ribozyme activity are reported. The relative affinities of divalent cations for the hammerhead ribozyme are determined by measuring their ability to release bound Mn2+. The EPR-detected Mn2+ competition studies give an order of apparent affinity of Mn2+ approximately Co2+ approximately Zn2+ > Cd2+ >> Mg2. This ordering generally follows the trend of maximum rates of cleavage determined at pH 7.0, 0.1 M NaCl, and saturating metal concentrations, of Mn2+ > Co2+ > Cd2+ > Mg2+. The maximum rate is observed for Mn2+ under these conditions and may be related to the high affinity, low pKa and low deltaHhyd of this ion. Substitution of phosphorothioates 5' to each of the nine adenosines in the enzyme strand yields a change in the Mn2+ binding properties of the hammerhead complex. In the phosphorothioate-substituted hammerhead complex, eight to nine Mn2+ bind in two types of classes: 'type 1' (n = 1+/-0.3, Kd = 1.1+/-1 microM) and weaker 'type 2' (n = 7.7+/-0.3, Kd = 125+/-27 microM). The multiple phosphorothioate substitutions result in the loss of two to three of the higher affinity sites observed in the unmodified ribozyme. Metal competition studies with the phosphorothioate-substituted ribozyme indicate that the relative affinities of the metals are Cd2+ > Zn2+ > Co2+, Mg2+ with the number of Mn2+ displaced and apparent affinity of the thiophilic Cd2+ most affected by the phosphorothioate substitutions.

IgG from neuropeptide FF antiserum reverses morphine tolerance in the rat.

Previous studies suggest that neuropeptide FF (NPFF) plays a role in opiate dependence and subsequent abstinence syndrome. The present study assessed the role of NPFF in opiate tolerance. Third ventricular injection of IgG from NPFF antiserum restored the analgesic response to i.c.v. morphine in morphine-tolerant rats (radiant heat tail flick test). IgG from control serum failed to produce this effect. In opiate-naive rats, however, the same treatment with IgG from NPFF antiserum did not affect the analgesic response to i.c.v. morphine. Thus, immunoneutralization of NPFF appears to selectively restore morphine sensitivity in opiate-tolerant animals. These results support the hypothesis that endogenous NPFF contributes to opiate tolerance.