Rm Br Research Articles

Superoxide Dismutase Inactivation by Radiation-Induced Radicals: Evidence for Histidine Residues in the Active Site

The inactivation of superoxide dismutase from bovine and human erythrocytes brought about by ionizing radiation has been studied. Both enzymes have similar radiation sensitivities, but, whereas the solvated electron is almost completely ineffective as an inactivating species, the probabilities of an OH radical or H atom inactivating a native enzyme molecule at pH 7.2 are about 0.04 and 0.1, respectively. H atoms are more effective when the enzyme copper is in the cuprous state, suggesting a conformational difference between the two oxidation states of the enzyme. Inactivation by ${\rm Br}_{2}{}^{-}$ radicals is negligible at pH 7 but increases sharply above pH 10. The effect of pH upon enzyme inactivation by ${\rm Br}_{2}{}^{-}$ has been compared with pH effects upon the rate and product absorption spectrum of the ${\rm Br}_{2}{}^{-}-\text{enzyme}$ reaction. In this way, ${\rm Br}_{2}{}^{-}$ was shown to inactivate the hol...

BrO Disappearance in the Pulse Radiolysis of O 2 +Br 2 and N 2 O+Br 2 Systems

The BrO transient formed during the pulse radiolysis of ${\rm O}_{2}+{\rm Br}_{2}$ mixtures decayed according to second-order kinetics, and the rate constant decreased slightly as O2 pressure was increased from 400 to 1560 Torr. Besides the variation with pressure, the BrO recombination reaction exhibited an initial phase in the time regime 3-50 μsec under certain experimental conditions during which BrO disappearance occurred at a faster rate. In the pulse radiolysis of ${\rm N}_{2}{\rm O}+{\rm Br}_{2}$ mixtures, the kinetics of BrO disappearance were found to be sensitive to the dose. In the lower dose range used in this work, the second-order rate plots were linear and BrO decay was invariant with pressure. With mixtures irradiated to a higher dose, BrO decay was also rapid but did not follow simple kinetics. The molar extinction coefficient of BrO was measured at three wavelengths in the near-uv region by determining the amount of ${\rm Br}_{2}$</tex...

The Primary Species Yields in the 60 Co g-Ray Radiolysis of Aqueous Solutions of H 2 SO 4 between pH 7 and 0.46

$G({\rm H}_{2}{\rm O}_{2})$ was measured in aqueous solutions containing different low concentrations of ${\rm O}_{2}+{\rm Br}^{-}$ and $G({\rm H}_{2})$ was measured in dilute solutions of KBr at d...

Topography of nucleic acid helices in solutions. IV. Effect of polyamines on RNase-catalyzed hydrolysis of polyadenylic acid.

AbstractThe effect of polyamines on the ribonuclease‐catalyzed hydrolysis of polyriboadenylic acid, cytidine‐2′,3′‐cyclic phosphate, and cytidylyl‐3′,5′‐adenosine phosphate (CpA) is reported. It is found that the salts, (I) \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_3 \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_n \mathop {\rm N}\limits^ + {\rm H}_3 \cdot 2{\rm Br}^ - $\end{document} inhibit the rate of hydrolysis of polyadenylic acid, whereas the hydrolysis of cytidine‐2′,3′‐cyclic phosphate, and CpA is accelerated. It is concluded that polyamines inhibit the RNase‐catalyzed hydrolysis of polyadenylic acid by binding to adjacent phosphate anions of the polynucleotide. The effect of other polyamines, i.e., the substituted salts (II) \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm RMe}_2 \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_n \mathop {\rm N}\limits^ + {\rm Me}_2 {\rm R} \cdot 2{\rm Br}^ - $\end{document} (where R = Me, Et, Pr, Bu, Pen, and —CH2CH2OH), (III) \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Et}_3 \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_n \mathop {\rm N}\limits^ + {\rm Et}_3 \cdot 2{\rm Br}^ - $\end{document}, spermidine, and spermine, on the RNase‐catalyzed hydrolysis of polyadenylic acid was studied at 37 and 50°C. At 37°C., maximum inhibition of the hydrolytic reaction occurs at n = 4 for the salts I and II. At 50°C., maximum inhibition of the RNase‐catalyzed hydrolysis of polyadenylic acid occurs at n = 3 for the unsubstituted salts I and the salts II where R = Et, and shifts to n = 2 for the salts II where R = Pr. Increasing the size of the substituent R of the salts, II, enhances the degree of inhibition. Substituting —CH2CH2OH for Et or Pr of the salts, II, decreases the extent of inhibition. Spermine and spermidine interact at very low concentrations with polyadenylic acid, causing significant inhibition of the RNase reaction. The result suggests that they interact with four and three adjacent negative charges of the polynucleotide, respectively. It is concluded that the salts, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_1 {\rm R}_{\rm 2} {\rm R}_{\rm 3} \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_n {\rm NR}_{\rm 1} {\rm R}_{\rm 2} {\rm R}_{\rm 3} \cdot 2{\rm Br}^ - $\end{document} interact with polyadenylic acid by electrostatic, hydrogen bonding, and hydro‐phobic forces. The electrostatic and hydrogen‐bonding interactions are important for binding the salts where R1R2 and R3 are small, i.e., H. Hydrophobic interactions are very important in binding the highly substitutde salts (II and III). The above results are compared with those obtained from the melting of rA–rU and rA–rU2 in the presence of the salts I and II. The following conclusions may be made: (1) the surface of a multistranded helix is more polar than that of the single strand; (2) the Tm of a helix–coil transition in the presence of the diammonium salts depends mainly on the interaction of the latter with the helix; (3) the overall structure of polyadenylic acid at pH 6.20 does not appear to change significantly upon forming the multistranded helices, rA–rU and rA–rU2.