Abstract
Abstract It has been shown that the enzymic addition of valine to valine transfer ribonucleic acid (tRNA) of Escherichia coli is exceedingly sensitive to alcohol or salt concentrations and that the rate of the reaction is predictable from the Debye-Huckel equations, if it is assumed that there are somewhat more than 4 positive charges and 4 negative charges involved in the rate-determining step. (For instance, the binding of the tRNA to the ligase and the rate of the subsequent reaction may be increased 3-fold by 10% ethanol or decreased 6-fold by 0.15 m NaCl.) The reaction has been found to be base-catalyzed, tris-(hydroxymethyl)aminomethane, imidazole, and NH4+ being stimulatory at low concentrations but following the salt inhibition curve at concentrations above 0.1 m. It is noted that other enzymic reactions involving RNA show a strong salt or solvent dependence of the same magnitude and kind. It is concluded that, although van der Waals' forces, hydrogen bonds, and hydrophobic bonds may determine specificity, the binding of an RNA molecule to an enzyme also requires a great deal of ionic bonding.
Highlights
Valine transfer ribonucleic acid of Escherichia co2i ethanol appears to reduce V, for the over-all reaction, the is exceedingly sensitive to alcohol or salt concentrations &I is lowered g-fold, and, at low tRNA concentrations, the and that the rate of the reaction is predictable from the rate of aminoacylation is increased a-fold
Debye-Htickel equations, if it is assumed that there are considered that charge-charge interactions were involved and somewhat more than 4 positive charges and 4 negative that the lowered dielectric constant of the ethanol medium was charges involved in the rate-determining step
(hydroxymethyl)aminomethane, imidazole, and NH4+ being prediction of the effect of conducting this reaction in the presence of varying concentrations of ethanol is not possible, but collateral reasoning would require that an increase in dielectric constant due to added salt might have an effect on binding similar to that predicted by the Debye-Htickel approximation
Summary
The change in K, depends directly upon the amount of alcohol. It has been shown that the enzymic addition of valine to tRNA to ligate and the rate of aminoacylation. (hydroxymethyl)aminomethane, imidazole, and NH4+ being prediction of the effect of conducting this reaction in the presence of varying concentrations of ethanol is not possible, but collateral reasoning would require that an increase in dielectric constant due to added salt might have an effect on binding similar to that predicted by the Debye-Htickel approximation. Recent work from these laboratories [1] required the measurementof o-phenanthrolineinhibitionof threereactions of aminoacyl transfer ribonucleic acid ligases ((AMP), EC 6.1.1.9), i.e. the catalysis of ATP-PPi exchange, the formation of [WI-valine hydroxamate, and the formation of [i4C]-valyl-tRNA.l. In order to maintain adequate concentrations of dissolved phenanthroline, it was necessary to conduct each reaction in the presence of loo/, ethanol. Other experiments with the same system were designed to test this relationship, which could be of considerable significance in the regulation of cellular metabolism
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