Adenosine 5’-triphosphate: Dephosphorylation promoted by Co(III) complexes and metal ion/polyamine systems

Abstract

Three model systems for the metal ion-dependent enzymatic hydrolysis of ATP have been examined.

The metal ion/ATP system, La('3+)/ATP, was examined at pH 7.6 and 13. Rapid hydrolysis and formation of pyrophosphate was observed at pH 13. The rate enhancement was by a factor of about 300. At pH 7.6, however, a slower rate of hydrolysis of ATP was noted in the presence of La('3+).

The Co('3+) complex/ATP system was used to form substitution inert Co('3+)-ATP complexes. From ('31)P NMR and HPLC studies, various mixtures of isomers are believed to exist in solution. The dephosphorylation of ATP promoted by the Co('3+) complexes has pointed to the importance of formation of a dinuclear Co('3+)-ATP complex and/or coordinated hydroxide for rate enhancement.

The third model system examined resembled its biological counterpart, M('2+)/enzyme/ATP. The model system, M('n+)/polyamine/ATP, was compared with M('n+)/ATP and polyamine/ATP systems. The twenty four-membered ring macrocycle 1,4,7,13,16,19-hexaaza-10,22-dioxocyclotetracosane, which is the most efficient among the polyamines examined in dephosphorylating ATP, was used in the presence of various metal ions (Zn('2+), Cd('2+), La('3+), Mg('2+), Ca('2+)) to investigate the dephosphorylation and complexation of ATP at pH 7.6. A phosphoramidate intermediate was observed only for this polyamine and has proven the reaction to be under strict structural control. The importance of certain metal ions (Ca('2+), Mg('2+) and La('3+)) both in the synthesis of pyrophosphate from the reaction of the phosphoramidate and inorganic phosphate (phosphorylation) and in the dephosphorylation of ATP in the presence of a polyammonium macrocycle was demonstrated. The dephosphorylation of ATP was enhanced by a factor of about 845 in the presence of La('3+) and 24 -N(,6)O(,2). The ternary complexes, M('n+)/ 24 -N(,6)O(,2)/ATP, were examined using ('31)P and ('13)C NMR techniques.