The interaction of ‘soluble’ ribonucleic acid, magnesium ions and sulphydryl groups in the control of amino acid-dependent pyrophosphate-exchange reactions

Publisher Website
Google Scholar
Abstract
The pyrophosphate-exchange reactions which are catalysed by rat-liver preparations and depend upon leucine or isoleucine are profoundly modified by "soluble" RNA and by changes in Mg concentration. The preponderant influence is exerted by the terminal nucleotide sequence of the "soluble" ribonucleic acid. Lysine-dependent pyrophosphate exchange occurs only at relatively high Mg concentrations and is not greatly influenced by "soluble " RNA. The transfer of [14C]lysine to "soluble " RNA is catalysed more rapidly by "recombined" systems than by pH 5.0 fractions and may be related to the inability of the enzyme to react with low concentrations of Mg, and to the presence of an inhibitor. The terminal nucleotide sequence of "soluble" RNA may be concerned in the protection of a labile, essential site associated with the activating enzyme. The leucine- and lysine-activating enzymes show highly individual responses to activators and inhibitors of sulphydryl groups. The possible role of the labile site in the reaction mechanism is discussed.