Metal Ions For Catalytic Activity Research Articles

Putrescine-insensitive S-adenosyl-L-methionine decarboxylase from Tetrahymena pyriformis.

Extracts of Tetrahymena pyriformis contain a soluble S-adenosyl-L-methionine decarboxylase which, in contrast to the enzyme from most eukaryotic organisms, is not stimulated by putrescine or spermidine. The protozoan adenosylmethionine decarboxylase, unlike the putrescine-insensitive enzyme form Escherichia coli, did not require any metal ions for catalytic activity either. Adenosylmethionine decarboxylase from Tetrahymena resembled the prokaryotic enzyme as far the inhibition by methylglyoxal bis(guanylhydrazone) was concerned, but behaved more like putrescine-activated enzyme in regard to the inhibition by 4-bromo-3-hydroxy benzyl-oxyamine. Adesylmethionine decarboxylase from rat liver, baker's yeast, E. coli and Tetrahymena were strongly inhibited by S-methyladenosylhomocysteamine (decarboxylated adenosylmethionine), the product of the reaction. The function of adenosylmethionine decarboxylase from Tetrahymena like that of the enzymes from other organisms appears to be closely connected to the synthesis of spermidine.

Selectivity in the metal-complex-catalyzed decarboxylation of oxaloacetic acid and a role of metal ion in an enzyme system.

Abstract The catalytic action of metal ions in the presence of various coordinating agents and a role of metal ions for the activations of an enzyme in a decarboxylation reaction were investigated. Many of the ligands studied decreased the catalytic activity of metal ions. However, α,α′-dipyridyl selectively enhanced the catalytic activities of divalent metal ions, except Cu2+. The activity of Cu2+ was specifically enhanced only with histidine and its derivatives. Histidine destroyed Ni2+ and Co2+ catalysis. The specific enhancement may be due to the increase in the electronegativities of the metal ions with dπ (metal)-pπ(ligand) back donation and to the stereo-configuration of the metal complexes. The catalytic behavior in these metal ion coordinating agent systems was different from that in the metal-enzyme systems. It was assumed that the activation of enzyme resulted from the change in the configuration of enzyme by the coordination of metal ions, and not from the catalytic action of metal ions enhanced by the coordination of enzyme. This was supported by the fact that the catalysis of compounds containing amino groups, active sites of enzyme, remarkably depended on the stereo-configuration. In the enzyme-model system, Mn2+ was generally preferable to Cu2+ and Ni2+. The catalytic actions of Cu2+ and Ni2+ were lowered by the complex formation with the active sites. This may solve the question why, in enzymatic reactions, Mn2+ having small complex-forming ability is more selective and effective than Cu2+ and Ni2+ with large complex-forming abilities.

Acidity and Catalytic Activity of Metal Ions

Acidity and Catalytic Activity of Metal Ions